electrical systems on meriden triumphs v3.0

Version 3.0 Nov 2009

DE-MYSTIFYING ELECTRICAL SYSTEMS ON MERIDEN TRIUMPHS

Version 3.0

By Pete Kinlyside – TriumphRat.net “OzBloke”, Melbourne, Australia

This paper attempts to explain the intricacies of Meriden Triumph electrical systems. The

idea for the paper was born from my own challenges with these systems, and from the many

electrical questions being raised by other owners on the TriumphRat.net Classics web forum.

I’ve tried to explain how things work in two formats; the simple non-technical format, and

the deeper technical format. It’s not meant to replace workshop manuals, but to

supplement them. Hopefully it will help those who want to maintain and fault-find these

sometimes frustrating but always amazing older bikes.

Contents Page

1. Common Terms .................................................................................................. 2

2. Diagnostic Table ................................................................................................. 3

3. Ignition Systems ................................................................................................. 7

3.1 Simple Science ............................................................................................ 7

3.2 Extra-Technical Explanation........................................................................ 8

3.3 Faults in the ignition system ........................................................................ 9

3.4 Points ........................................................................................................ 10

3.5 End-to-end testing. .................................................................................... 12

3.6 Boyer Electronic Ignition Systems ............................................................. 13

3.7 Fault-finding a Boyer setup ....................................................................... 14

4. Charging system ............................................................................................... 16

4.1 Rectifier .................................................................................................... 16

4.2 Fault finding bridge rectifiers .................................................................... 18

4.3 Zener Diode............................................................................................... 19

4.4 Testing a Zener Diode ............................................................................... 20

4.5 Alternator ................................................................................................... 21

4.6 Testing the Alternator stator ...................................................................... 21

4.7 Battery ....................................................................................................... 22

4.8 End-to-end Charging system testing .......................................................... 23

5. Indicators .......................................................................................................... 23

6. Lighting System ............................................................................................... 24

6.1 Faults in the lighting system ...................................................................... 25

7. Horn ................................................................................................................. 26

7.1 Fault finding a horn ................................................................................... 26

8. A Few Tips ....................................................................................................... 27


1. Common Terms

First, some terms you might see, read or hear when working on your bike, and which I use in

this paper

Term Meaning

Earth The common return path for electrical current, usually the frame of

the bike, plus the engine. Aka: frame, chassis or ground.

Voltage The measure of electricity force or “pressure”, measured in Volts

Current The measure of electricity flow, stated in Amps

Resistance The measure of resistance of a certain component to current flow,

measured in Ohms ( Ω ), or Kilohms (1000 Ohms or KΩ), or Megohms

( 1 million ohms or M Ω)

Short aka. Short circuit. A path for current that bypasses vital components

– usually associated with a fault, resulting in high current flow, burnt

wires, blown fuse, bad smells, and sometimes fire.

Open Circuit A broken path, which does not allow current to flow, Usually

associated with broken wires, poor connectors, blown fuse, or faulty

components.

High-tension Aka HT. The high voltage output from the coil. The connection from

the secondary winding of the ignition coil to the spark plug – the

spark plug lead.

Component An electrical part that performs a function. Examples are coil, switch,

battery, rectifier, diode, lamp,

RFI Radio Frequency Interference. Electronic noise radiating from

electrical components due to magnetic fields generated by current

flowing through a conductor. Can be heard as “clicks” on an AM

radio.

RFI can be closely associated with EMI – electromagnetic

interference, where voltage spikes are introduced into circuits from

radiated energy, causing failures or errors in computerised

equipment – eg computer-based ignition systems.

Wire A physical connection between two components, usually with a

centre conductor of copper, and an outer sheath of plastic or cotton,

and a metal connector at each end. Aka – cable, lead. Wires gathered

together in a larger common sheath (or bound with tape) are known

as the loom.

Multimeter An analogue or digital meter used as test equipment, capable of

several working modes, such as Resistance, Voltage, Current, Diode

check.


2. Diagnostic Table

The table is used to diagnose basic problems with the electrics on Meriden Triumphs.

Positive earth is assumed.

Symptoms may be noticed en mass or individually. Suggested actions for a particular

problem do not align with specific symptoms, but should be taken in the order shown until

the problem is resolved.

Problem Symptoms Suggested Actions Refer to

Section

No Power Oil light does not

come on when

ignition switch

turned to On.

Engine will not

start.

No lights

No brake light (with

ign on and brake

lever pulled or

brake pedal

pressed)

1. Check fuse – if in doubt,

replace with a new 20A fuse.

Clean the terminals inside the

fuse holder.

2. Check battery voltage – should

be =>12.3V. If lower than

11.5V, re-charge or replace

battery.

3. Check battery connections are

clean and tight.

4. Check connection to frame

from battery is clean and tight.

5. Check connections to ignition

switch.

Power, but no

lights

Oil light comes on

with Ign switch

turned On, but no

lights (headlight,

tail light, pilot light)

1. Check wiring to Ign switch

2. Check lighting switch

3. Check globes

4. Check / clean/ tighten

connections to lights, including

earth/frame connections

5. Check/clean handlebar

switches

Power, but no

spark (Points

ignition)

Engine will not

start.

No spark at either

plug (with plugs out

and resting on head

fin, with HT lead

still connected).

1. Check power to Negative of

each coil with Ign switch On.

Should be -12V or greater. If

not, check wiring from Ign

switch, via kill switch (if fitted)

to coils.

2. Check Positive terminal of

each coil. Should read -12V

with points for that cylinder


open, and 0V with points

closed.

3. If constant 12V, check wiring

to points for an open circuit –

eg dirty or broken connector,

broken wire.

4. If constant 0V, check wiring for

a short to frame, or points wire

contacting earth inside timing

well.

5. Check coils primary windings

for continuity.

Power, but no

spark (Boyer)

Engine will not

start.

No spark at either

plug (with plugs out

and resting on head

fin, with HT lead

still connected).

1. Check power to EI system. If

not -12V, check wiring from

Ign switch via kill switch (if

fitted) to EI unit.

2. Check power to negative

terminal of 1st coil (coils are

wired in series). Should be -

12V after 1 kick, and last for up

to 5 seconds unless another

kick occurs.

3. If constant -12V, check

connection to EI unit, or EI unit

needs to be checked/replaced.

If 0V, check pickup wiring.

4. Check the wire connecting the

Positive terminal of 1st coil to

the Negative terminal of 2nd

coil

5. Check earth connection from

Positive terminal of 2nd coil.

6. Check both coils for primary

winding continuity

Power, but no

spark on one

cylinder only

(Points ignition)

Engine runs rough,

with no power.

One cylinder

cold/warm, with

other one hot.

1. Check spark plug (swap with

other cylinder). If fault moves

cylinders, replace plug

2. Check HT plug lead (swap with


cylinders, replace HT lead.

3. Check coil has power to

negative terminal.

4. Check points opening/closing

5. Check wiring from points to

coil positive terminal.

6. Check connection to

condenser.

7. Check coil windings

Power, but no

spark on one

cylinder only

(Electronic

ignition)

Engine runs rough,

with no power.

One cylinder

cold/warm, with

1. Check spark plug (swap with


cylinders, replace plug

2. Check HT plug lead (swap with



other one hot. cylinders, replace HT lead.

3. Check coil windings

Charging system

not working

Engine runs poorly

or stops when

battery gets low.

Battery needs to be

charged after every

ride.

Ammeter (if fitted)

showing negative

(discharge) >3

Amps.

Battery voltage

with engine running

at 3000 RPM is 12.5

V or lower, and

does not rise or

drop with engine

revs

1. Check connections from

alternator stator to rectifier.

2. Check connections from

Rectifier to battery, via fuse

3. Check earth connection to

rectifier.

4. Check battery earth/frame

connection

5. Check alternator stator

continuity.

Charging system

weak

Can’t run for

extended periods

with headlight on,

else engine runs

poorly or stalls.

Battery voltage

with engine running

at 3000 RPM is

between 12.5V and

13.5V.

Ammeter (if fitted)

shows slight

discharge at

3000RPM with

headlight on.

1. Check for poor connection

between alternator and

rectifier, looking for corroded

or broken metal parts in

connectors, and frayed wires.

2. Check, clean and tighten blade

connectors on rectifier, and

check wiring to battery (via

fuse, and ammeter if fitted).

3. Check rectifier

4. Check alternator stator for

continuity.

Charging system

on steroids

Battery gets hot

Battery boils off

liquid, and needs

constant topping

up.

Battery voltage at

high revs goes over

15V

Blowing light globes

regularly.

Ammeter shows

charge of greater

than 4 amps for

more than 10-15

1. Check connections to Zener

diode.

2. Check earth connection on

Zener diode.

3. Check Zener diode for proper

operation.

4. If using after-market regulator,

get it tested, or replace it.


mins.

Indicators – not

lighting at all

When indicator

switch set to L or R,

indicators do not

come on at all

1. Check indicator globes

2. Check earth connections to

stalks

3. Check wiring from handlebar

switch to globe holders.

4. Check wiring from Ign switch

to flasher can, and from

flasher can to handlebar

switch.

5. Check/replace flasher can

Indicators – on

constant (not

flashing)

When indicator


indicators come on

solid but do not

flash

1. Check battery voltage.

2. Check for correct wattage

indicator globes (21W)

3. If this only happens at idle

revs, check charging system

(weak)


Indicators – slow

flash

When indicator


indicators come on

but flash slowly

1. Check for correct wattage

indicator globes (21W).

2. Check charging system

Indicators – fast

flash

When indicator


indicators come on

but flash too

quickly

1. Check for blown globe, or

broken connection to one

globe

2. Check for incorrect wattage

globes


Horn Not working –

clicking sound when

horn button

pressed

1. Use adjustment screw on rear

of horn to obtain correct tone.

Screw clockwise.

2. Check for poor connections

and frayed wires

Horn Not working – no

sound

1. Check connections from horn

switch to horn, and from horn

to earth. Note that earlier

bikes switch the earth via the

handlebar switch, while later

models switched the power.

2. Check adjustment screw –

screw until sound is heard

when pressing button.

3. Check horn internally for poor

contact points and mis-

adjustment.


3. Ignition Systems This section explains the inner working of Meriden Triumph ignition systems, from the basics

such as the theory behind the system, to the more advanced areas like Boyer ignition

systems.

Ignitions systems are built from a combination of components. For most older bikes (except

magneto ignition systems), these are:

• The battery

• The fuse

• The ignition switch

• The engine kill switch

• The points (aka breaker points, contact points)

• The condenser(s) (aka capacitor)

• The coil(s)

• The spark plug(s)

• The wires between the various components, in particular the plug leads.

For the sake of simplicity, take it for granted that I’m explaining things using a single cylinder

at this point. Not much difference with a twin or triple cylinder engine, where most

components are duplicated, except when you get into the electronic systems such as Boyer

or RITA.

3.1 Simple Science

One terminal of the battery is connected to earth. Most modern bikes are negative ground,

while the older Meriden Triumphs are positive ground. Positive earth (or positive ground)

means that the positive terminal of the battery is directly wired to the frame and engine of

the bike to provide the return path for the electrical current, and the negative terminal of

the battery is the “active” terminal.

The other terminal of the battery is wired to the fuse, then from the other side of the fuse to

the ignition switch, and from there to the kill switch (if fitted), and from the kill switch to one

side of the coil (in the Meriden case, the negative terminal of the coil). With the ignition

switch off, no current flows to the coil, and no spark can be produced. With the ignition

switch and the kill switch both in the “on” position, 12 volts is applied to one side of the coil.

The coil is basically a 1:100 transformer. It has a primary winding, being the two screw/blade

terminals on top for positive and negative 12 volts connections. The other half is called the

secondary or high tension winding. One end of the secondary winding connects to the

negative terminal, while the other end connects to the insulated cup connector on the top,

into which the plug lead is connected.

The set of points, operated by the camshaft, acts as an on/off switch for the positive side of

the coil to earth. When the points are closed, current flows from the battery, through the

fuse, through ignition and kill switches, through the coil, through the points contacts, to the

engine casing, and finally back to the positive side of the battery via wires and/or frame. At

this stage, the condenser, which is wired across the points, is not charged, as the points

short it out. Diagram 1 illustrates the components and the current path.


This current flow quickly creates an electromagnet inside the coil. While the points are

closed, this magnetic field remains stable. At a point in the rotation of the camshaft, a lobe

on the points cam causes the points to open. Current is no longer flowing through the coil,

and the magnetic field quickly collapses. This collapsing magnetic field causes a voltage to be

induced or generated in the secondary winding. The condenser comes into play now, as it’s

no longer being shorted by the points. It has a dual function – to help pump up the primary

voltage, and to drastically reduce arcing across the points. The primary voltage goes up to

around 300-400 volts, and the secondary voltage leaps to 20-30 thousand volts.

This secondary voltage is sufficient to jump the gap between the spark plug centre electrode

and the side (ground) electrode, and current flows from the coil secondary, through the

spark plug, through the engine to the frame, through the condenser, to the negative

terminal of the coil. When the voltage being developed by the collapsing field inside the coil

is no longer sufficient to jump the gap, the spark stops.

3.2 Extra-Technical Explanation

As the points open, the magnetic field around the primary winding of the coil begins to

collapse. This induces a voltage across the secondary and primary windings. The condenser

initially acts as a short until it starts to charge. This stops arcing across the points contacts, as

the potential difference between the points grows comparatively gradually. As the voltage

builds across both the secondary and primary, no current is yet flowing through the

secondary, as the current path is not yet established across the spark plug gap. Around 400

volts can be developed across the primary winding as the condenser becomes fully charged.

Depending on the spark plug gap, and the state of the fuel vapour /air mix between the plug

electrodes, at a certain voltage, the vapour will ionise, and allow current to pass. This

commences the spark. As the current flows through the secondary winding, the condenser

discharges through the primary, thereby inducing more voltage across the secondary, which

elongates the spark time. This “loop” effect, or ringing, continues in a decreasing cycle until

the condenser no longer holds sufficient charge to induce enough voltage in the secondary

to maintain the ionisation of the plug gap, which is when the spark stops. Without the

Battery

Fuse

Ign Sw Kill Sw

Coil

Condenser

Points

Spark

Plug

DIAGRAM 1

Current Flow


condenser, the spark will be of very short duration, and quite weak. The points will also arc

on each opening, causing pitting of the contact surfaces and eventual breakdown.

3.3 Faults in the ignition system

Note: Voltages in the ignition circuit can be harmful, and painful! Do not touch connectors

or components with the engine running. Resistance testing of ignition components must be

done with the fuse out and ignition switch off, and preferably with the component

completely removed from the electrical circuit.

Testing of the condenser can be done by using a multimeter on the highest resistance (20M

Ω - 20 Mohms) range. Take one of the bike electrical connections off the condenser, and

connect the probes across the component, watching the meter display as you connect the

probes. The meter should indicate a low initial resistance, with a rapid increase in resistance

as the condenser charges over a period of a few seconds. The meter should, after no more

than 5 seconds, indicate infinite resistance. If it shows some steady high resistance (eg

10Mohms), or slowly decreases after initially going high, the condenser needs to be

replaced. Make sure your fingers aren’t touching the metal portion of the probes when you

do this test, as it will give false readings. The ignition condensers can be tested in either

polarity, with the same results. If reversing polarity immediately after a test, the initial meter

reading may be false due to the charge on the condenser from the meter.

Coils can go faulty in a number of ways. The primary can go open circuit due to vibration or

heat (continuous current for extended periods – burnout). The secondary can go open, or

can short turns (a current path between layers of the winding, resulting in greatly reduced

output), or a short to the outer case.

Testing of the coil is a 4 step process. First take all connections off the coil, including the

high-tension lead (plug lead). Using a multimeter on low resistance range (200Ω), check the

resistance between the two low tension (primary winding – 12 Volt) connectors. 6 volt coils

should read around 2 to 2.5 ohms. 12 Volt coils should read between 4 and 5.5 ohms. If

higher, it could be faulty or a higher voltage (eg 24v) coil. If lower, shorted turns are the

most likely culprit – replace.

Next, check the secondary winding by a resistance (meter on 20KΩ range) check between

the negative 12V terminal and the high-tension output (the brass connector inside the tower

where the plug lead goes). This should be around 5 to 6 KΩ.

The last check is between either the negative terminal, or the high tension terminal, and the

metal casing, with meter on highest Ω range. Should be infinite resistance from either point.

Again, make sure your fingers aren’t touching the probes, as a false reading will result. If not

infinite resistance, the coil has a short to the case, and should be replaced.

Spark plug leads can be tested by checking resistance from end to end. Meter on 20K Ω

range for Suppressor leads, or 200 Ω for copper core leads. For copper core high-tension

leads, resistance should less than 1Ω between the metal connectors at the ends. Radio

frequency interference suppression leads can be identified by either reading the writing on

the lead (it will say it’s “suppressor lead” or similar), or by taking the rubber boot off one

end and looking where the lead enters the metal connector. Suppressor lead centre

conductor looks like a number of strands of tiny fishing line coloured dark grey or black.

Suppressor leads will measure around 5 K Ω for the approx 600 mm length. Any higher,


they are possible faulty or the wrong type, and they start to limit the high-tension current to

the point where the spark strength is degraded.

Similarly, spark plugs can be tested with a meter. Good idea to give the firing end of the plug

a scrub with a brass or wire brush to remove any carbon or burnt oil deposits that could give

a false reading. Suppressor plugs have an in-built resistor to limit the current of the high-

tension system, thereby limiting the RF interference caused by the ignition system. Plugs

without in-built resistor should read less than 1 Ω between the top cap (where the lead

plugs on) and the centre electrode at the firing end. The suppressor plugs will read around 4

to 5 K Ω between top cap and the centre electrode. Both types should read infinite

resistance between top cap or centre electrode and the metal casing. If in any doubt,

replace the plugs – they’re fairly cheap.

Total suppressor resistance, from the coil end of the plug lead to the centre electrode at the

firing end of the spark plug, should not exceed 5 K Ω. Any more than this and the spark may

be weakened to the point where misfires or no spark could occur under normal operating

conditions. Copper core plugs leads will give the more powerful spark, but may cause

interference on nearby TV’s, radios, computer equipment, etc. If you use a computerised

ignition system or other electronic equipment on your bike, use suppression leads or

resistance plugs to a maximum of 5 K Ω resistance. It’s not a good idea to use both

resistance plugs and suppressor leads together. One or the other will be fine for suppressing

RFI.

3.4 Points

There are two types of points plates used on older Triumphs, both shown below.

The first is the older style, where the condensers are mounted on the points plate itself, and

the centre conductor of each condenser is used to provide a connection point for both the

points spring, and the wire to the coil. Note the small plastic tab between the condenser and

the spring – this stops the spring metal, or the connector on the wire to the coil, shorting to

the case of the condenser (earth). The plastic tab also extends to stop wires or connectors

shorting to the side of the points well in the timing case.


The newer style of points plate is shown below.

Note that the condensers associated with the newer style of points plate are mounted on

the bracket holding the coils, not on the points plate. There is a small fibre washer between

the outer casing of the condenser and the coils plate, stopping the outer casing from

shorting to earth. The centre positive pole/stud of the condenser is used to secure the

condenser to the plate, and the wire to the coil is connected to a blade connector soldered

onto the outer casing of the condenser.

The most important thing to note about this newer type of points plate is the insulators

between the base plate, the stud holding the points spring, and the point springs itself. See

Diagram 2 below. If the connector on the wire from the coils touches the stud or the nut, it

will short out the points – no spark on that side and the coil will get really hot with the

ignition on. The wire connector must contact the points spring, but not the stud or nut.

Points can be checked by doing a resistance check between a) the point where the wire

connects to the points and b) engine metal (ground/earth). Note that the other end of the

points wire must be disconnected from the coil to do this test. 0 Ω for points closed, and

Points spring (cut-away to show detail of insulator)

Base plate

Insulating fibre washer

Insulating plastic washer with protrusion

Steel lock washer

Nut

Stud This type of connector…

slides in here

DIAGRAM 2


infinite resistance for points open. Note that the condenser may still be in circuit (if it’s

mounted on the points plate), so points open resistance reading may take a few seconds to

reach infinite.

3.5 End-to-end testing.

If all components check out OK, a fault in the ignition system is most likely to be a bad

connection or broken wire.

The following tests are done with the fuse in, and live 12 volts applied to the ignition

system. For safety, take the spark plugs out and rest them on the head with leads still

connected. This way, there’s no way the engine can start, and you can see if a spark occurs

at the plug. Keep your hands and other body parts away from the electrical components

and connectors. They get hurt if they get hit with ignition voltages. Make sure you have no

fuel or gas vapours in the vicinity, or fuel leaks. Have a fire extinguisher handy just in case.

Meter on 20V range. One lead on battery earth (positive terminal on older British bikes) or

on a good bare metal part of engine or frame.

Ignition switch on, kill switch to run. Place the other meter probe on the power side of the

coil primary (negative terminal on older bikes). Meter should read between 12.5 and 13.8

volts. If lower (eg 11 V), check state of battery. If no voltage reading, check the battery earth

connection, then the fuse, then the ignition switch, then the kill switch, and the cables and

connectors between all these components. You can use the meter probe to test for -12v

along this route.

Once you have -12V at the power side of the coil primary, rotate the engine until the points

are open. Measure voltage at the other primary connector on the coil (+ on older bikes) –

should be -12V. If not, could be an open circuit coil, or a shorted condenser, or a short circuit

to earth in the points cabling or points themselves. Most likely cause is the wire connection

to the actual points being frayed or misaligned, or a missing insulator on the stud holding

the points spring – the wire must connect to the points spring, but be insulated from the

mounting stud (see Diagram 2 on the previous page). Follow through by turning the ignition

off, and checking resistance of the coil primary, and the resistance between earth and the

points wire.

Once you get -12V on both sides of the coil primary with points open, rotate the engine until

the points close. You should now see 0 Volts on the points side of the coil primary (+ on

older bikes). If not (ie still seeing greater than 0.2 volts), then there is either a broken wire or

connector (open circuit) between the coil and the points, or the points are not closing

properly. Points not closing will usually be caused by mechanical misalignment, or by an

obstruction between the points contacts such as oil, dirt, corrosion, pitting/carbon, etc.

If all checks out OK, with fuse in, ignition on, kill switch to run, use the kickstarter to turn the

engine over. Check for spark at the spark plug (still resting on the head). If no spark at all,

check the plug lead and spark plugs as described previously.

A further check is the test for voltage at the plug end of the high-tension lead. Meter on 20V

range, ignition on, points open, one meter probe on battery earth/frame. DO NOT kickstart,

or close/open the points, or turn the ignition switch off, with meter connected to the plug

lead, you will damage your meter. Disconnect the plug lead from the spark plug, and

connect the other meter probe to the metal end of the lead. You should see around 10 to 12


V on the meter. If not, lead is faulty, or secondary winding of coil is open circuit. Check

components as described previously, and replace as required.

3.6 Boyer Electronic Ignition Systems

Electronic ignition systems available for motorcycles usually just replace the points, with

some added electronics to provide for spark advance. They still require coils to generate the

high-tension voltage for spark.

Diagram 3 shows a typical Boyer setup, using 2 coils.

The Boyer control box has 5 connections.

1. The -12 volt power input line - White

2. The -12 volt coil power output line - Black

3. The +12 volt line – Red

4. One pickup sensor line – Black/ yellow

5. The other pickup sensor line. – Black/white

Boyer control boxes need an absolute minimum of 10 volts to operate. If your battery is not

well charged, and unable to supply a minimum of 10 volts under load (ie with ignition on),

the unit will not operate.

Power is applied to the control unit once the ignition switch is turned on, and the kill switch

is in run. Power will not be applied to the coils until the first pulse is received from the

pickup sensor unit, which is mounted where the points used to go and using the points wires

to connect the pickup sensor unit to the control box. If pulses stop being sent from the

pickup sensor, the power to the coils will be cut off approximately 3-5 seconds later. This is

to stop coils being overheated and burnt out, and batteries being flattened, by continuously

feeding power to the coils when it is not required. The lowest RPM that the Boyer will

operate effectively is 200 RPM.

Battery

Fuse Ign Sw Kill Sw

Coil

Spark

Plug

DIAGRAM 3

Current Flow

Coil

Pickup Plate

Boyer

White

Black

Black

Red

Black/Yellow Black/White


Note that the coils are wired in series. That means the current path goes from the Boyer

control box, through one coil, then through the other coil, and then to earth. Wiring coils in

parallel will cause damage to the control box due to excessive current. The control box will

limit the coil(s) primary winding voltage to 400V, and with two coils wired in series, this

equates to 200 volts per coil. Depending on the coils used, this limiting may result in limited

output voltage to the spark plugs. Converting to 2 x 6V coils gets around this possible

problem – something to think about if you’re getting weak spark with a Boyer and 2 x 12V

coils. Some people prefer a single 12v coil with dual high-tension outputs.

Boyers fire both cylinders at once, at both the top of the compression stroke (when it should

happen), and at the top of the exhaust stroke (when it’s not required, but doesn’t hurt). This

makes the design simpler, and also assures matched ignition timing between twin cylinders.

The pickup sensor is simply two coils wired in series, and mounted 180 degrees apart, with

their centre metal cores protruding. Magnets are similarly set onto a rotor fitted to the

camshaft. As the rotor rotates, the magnets sweep close by the protruding metal cores,

which induces a small voltage in the coils. This voltage pulse is fed to the control box via two

wires, and is used to “trigger” the momentary disconnection of the negative power line from

the ignition coils (virtually the same as opening the points), creating spark.

When initially set up, the pickup sensor is timed at full ignition advance. When the engine is

running at idle, the spark is electronically retarded by approximately 10 degrees. As the

engine speed increases, less retardation is applied (more advance). Maximum advance (or

more precisely zero retardation) is reached around 5,000 RPM. Condensers are not required

in a Boyer setup.

Note that if the pickup sensor cable are wired in reverse (crossed over), the pulse received

will be the wrong polarity, and the control unit will actually sense the trigger pulse when the

magnets are leaving the pickups coils, rather than as they approach. This has the effect of

significantly retarding the spark (by around 50 degrees), and the engine will be virtually

impossible to start. You will see spark, and everything will look good, but the timing will be

way off. Make sure you get the polarities right from the sensor to the control box for the

black/yellow and black/white wires.

3.7 Fault-finding a Boyer setup

Note that the fault-finding methods described here are for a positive earth bike, with two

coils.

Boyer control boxes need an absolute minimum of 10 volts to operate. If the battery is not

well charged, and not able to supply at least 11.0 volts under load (ie. with ignition on), the

unit may not operate properly. Make sure you have a good battery in place before doing any

other fault finding.

Check the 12v power side by meter on 20V range, connecting one probe to battery earth.

Connect the other probe to the primary winding (12V) connector on the first coil that has

the black power wire from the Boyer. Take the spark plugs out and rest them on the head

with leads still connected. With ignition and kill switches on, rotate the engine with the

kickstarter. After 1 or 2 revolutions of the engine, you should see 12v on the meter. This will

return to zero volts after 5 seconds or so, so watch carefully.

Now check the pickup sensor. Take both the black/yellow and black/white wires out of their

connections to the Boyer control box. With meter on 200 Ω range, measure the resistance

between these two wires going to the sensor plate. You should read 132 Ω. If significantly


lower than 132 Ω, one of the sensor coils may be shorted, or the printed circuit board that

the coils are mounted on may have a short between tracks. If significantly more than 132 Ω,

or infinite resistance, there is probably a faulty connector between the control box and the

pickup sensor. Check the resistance of each wire from end-to-end individually, and check the

resistance of the sensor at the connector on the senor plate itself.

The last check you need to make is the wiring of the coils. With meter on 200 Ω, and ignition

off, check the resistance from the -12V primary connector on the first coil, to the +12V

connector on the other coil – that means across both coil primaries. For 2 x 12V coils

connected in series, you should read no more than 10 Ω . For 1 x double ended 12V coil, or

for 2 x 6V coils, you should read no more than 5 Ω . If more, it’s most likely the wire joining

the two coils together, but could also be a faulty primary winding on either coil.

If the power connections, coils connections, and the sensor checks above check out OK, and

you’re sure of the good state of the battery, the fault will probably be with the control box.

If it’s just been fitted, and not yet worked at all, check that the right connections are being

made to the control box, as per the Boyer instructions. With ignition on, if you disconnect

the two wires at the sensor plate (black/yellow and black/white) and tap them together

rapidly, you should see spark at the plugs

As mentioned previously, you should have no more than 5 KΩ total resistance on each plug

lead / resistor spark plug combination.


4. Charging system

The charging system on the Meriden Triumphs is quite simple. An alternator, a rectifier, and

a zener diode, along with the battery of course.

The alternator has two parts. A rotor, which is basically a strong magnetised cylinder

mounted on the outer end of the crankshaft, and a stator, which is a ring of coils on a

toroidal (donut-shaped) iron core, mounted around the rotor. As the magnetised rotor is

spun by the engine, it’s magnetic field “cuts through” the winding of the coils, generating a

voltage in the coil. Because of the rotation, and the north/south poles of the magnet, the

voltage alternates between positive and negative. When an electrical load is applied and

current flows, it is called alternating current, or AC (also why it’s called an alternator).

4.1 Rectifier

To be useful in a direct current (DC) environment such as bike electrics, this alternating

current must be changed (rectified) to direct current. This is the job of the rectifier. The

rectifier is basically 4 high current diodes wired in a Bridge Rectifier pattern, which converts

the positive/negative AC voltage from the alternator to all-positive or all-negative voltage.

Extra-Technical Information

Diagram 4 shows a typical bridge rectifier setup and corresponding waveforms. Please note

that I use the “electron flow” theory to explain operation.

Diodes only pass current in one direction – think of it as the current being able to go up the

“slope” of a diode, but not up the “cliff”. Looking at Diagram 4 above, when the AC voltage is

fed to the input, in one half of the AC cycle current is passed by the top left and bottom right

diodes, while the other two diodes are reverse biased and pass no current. In the other half

cycle, the top right and bottom left diodes are the ones forward biased and passing current,

while the other two are blocking current flow. This results in a Direct Current (DC) output

made up of both the positive and negative halves of the AC input.

Note that the older style rectifiers use the mounting bolt as the earth connection for the

positive DC output. The picture below shows a typical bridge rectifier.

-15

AC input from alternator DC output

-15

0

+15 0

DIAGRAM 4


The centre mounting bolt also provides the earth path. The positive output wire

(ground/earth) goes on the centre bolt at the top, the two wires from the alternator go on

the outer two of the three terminals grouped together, and the negative (live) wire to the

fuse goes on the centre connector of the three.

An alternative and cost-effective rectifier can be made using a common solid-state 25 Amp

bridge rectifier as shown in the picture below, available from your local electronics shop for

around $5.

Bolt the rectifier through the centre mounting hole to an L bracket, and mount the L bracket

where the old rectifier was. Connections are the same, except you might have to also wire

the positive (if system is positive earth) DC output to earth – the L bracket.

+

~

-


4.2 Fault finding bridge rectifiers

To test a bridge rectifier, the easiest way is to use a multimeter with a diode checker. This

will be indicated by a certain switch position on the meter, or a combination of switches,

showing the diode symbol. In this mode, the meter will show the voltage drop across a

forward biased diode, therefore the position of the probes is important when checking

diodes.

To eradicate the possibility of either the alternator or the rest of the bike electrics affecting

your testing, take the fuse out, and remove all the wires connecting to the rectifier. Be

careful to note which wires go where – you don’t want to put them back in the wrong place

or you’ll end up cooking some wiring.

You have 8 checks to do – forward and reverse on each diode in the set of 4. Use a

multimeter on Diode check mode.

Using Diagram 4 and the picture above as an reference, the first test would be putting the

red probe on the negative output connector, and the black probe on either AC input

connector. This will forward bias one of the left hand diodes, and you should read between

.400 and .700 on the meter. Test the other left hand diode by moving the black probe to the

other AC input connector. Reading should be very similar. Now reverse the two probes so

the black is on the negative output connector, and the red probe is on either AC input

connector. You should read infinite – “1 blank” on an LCD screen multimeter. Swap the red

probe to the other AC input connector to check the other diode.

Now test the right hand diodes by placing the black probe on the positive DC output

connector (may be the centre bolt/earth on the older rectifiers), and the red on either AC

input connector. Again, you should see .400 to .700 on the meter. Check the other diode by

swapping the red probe to the other AC input connector. Now check the reverse bias by

placing the red probe on the positive DC output, and the black probe on either AC input. You

should see “1 blank” on the meter.


If at any stage during this testing, you see something like “.003” or any similar low reading, it

means the diode being tested is faulty. The same diode will probably measure the same in

the reverse test, as it’s burnt out and imitating a piece of charcoal. If this is the case, it’s time

to replace the whole rectifier.

4.3 Zener Diode

The symbol for a Zener diode is shown here.

The Zener diode is basically a rudimentary voltage regulator, and is used to stop the

alternator/rectifier voltage getting high enough to cause damage to the battery, lighting

globes, coils, etc.

The zener is special in the sense that it acts as a normal diode in the forward biased state (as

explained in the Rectifier section – current can flow up the slope but not up the cliff), but in

the reversed biased state it will only block current until a certain pre-set limit is reached, and

then it will conduct. This limit on 12 volt bikes is set at 15.0V. Zeners used as voltage

regulators are wired in reverse-bias mode, and have high current and high power dissipation

characteristics. Zeners will have either a finned heatsink, or be mounted on metal in an area

of high air flow.

Extra-technical information

As alternator rotor speed increases, the magnetic lines of force cutting the windings of the

stator increase in frequency. This not only increases the frequency of the AC output, but also

the output voltage (amplitude). To protect electrical components, such as the battery from

overcharging, and the light globes from blowing, the voltage must be controlled.

As can be seen in Diagram 5 above (positive earth system), the AC output of the alternator is

applied to the rectifier, which converts the AC to DC. This DC is then applied to the battery

and the rest of the electrical system of the bike. The Zener is wired in reverse bias across the

main power feed out of the rectifier.

When the voltage at the output of the rectifier is less than 15 volts, the Zener is inactive, and

has no affect on the rest of the electrical system. If the DC voltage on the anode (the “cliff”

side) of the zener reaches the preset trigger voltage (15.0V) the Zener diode immediately

goes into the avalanche condition, and provides a very low resistance path to earth – almost

a dead short circuit. Current flows through the Zener to earth. This has the effect of rapidly

Zener Alternator

Rectifier

Battery

DIAGRAM 5

Rest of bike electrical load


reducing the voltage coming out of the rectifier. As the voltage goes below 15 volts, the

Zener goes back to passive state. Thus, the voltage coming out of the rectifier is limited to a

maximum of 15 volts. This is commonly known as a “crowbar” regulator.

4.4 Testing a Zener Diode

The simplest test you can do on a Zener diode is to check it with a multimeter in diode test

mode. It will act as a normal diode with the test voltage available through the multimeter. It

should show 0.400 to 0.600 on the meter when forward biased, and “1 blank” in reverse

bias. For Zeners meant for positive earth systems, the base stud or heatsink will be the

cathode (the pointy end of the triangle symbol), and the insulated blade connector will be

the anode (the flat end of the triangle – the “cliff face”).

The wire from the battery/rectifier should be disconnected. It’s OK to leave the Zener

mounted, as long as you can find a bare metal earth point to put your probe on. Multimeter

in diode test mode.

For positive earth systems: Red probe on Zener blade, black on earth - .4 to .6 reading. Red

on earth, black on blade – 1 blank reading.

For negative earth systems: Red on earth, black on Zener connector - .4 to.6 volts, Red on

connector, black on earth – 1 Blank reading.

If the Zener is faulty, it will usually show up as a short circuit (low readings in both

directions), and other problems with bike electrics will be quite evident – constantly blowing

fuses will be the main symptom.

To test the reverse turn-on voltage of the Zener, use the following test circuit. Please note

this is for Positive earth systems – that is, Zeners with the cathode being the base mounting

stud or heatsink.

See diagram 6. Wire two standard 9 volt batteries in series as shown – positive of one to the

negative of the other. These are the standard batteries that go into toys, smoke detectors,

multimeters, etc. In this test, it’s likely you will drain a fair bit of power out of them, so if you

have to go and buy some, get the cheapest you can find.

18.50

DIAGRAM 6


Once the batteries are wired together, use your multimeter on 20V DC range to make sure

the combined voltage is above 15 Volts.

Using a piece of wire, connect the stud or heatsink of the Zener to the positive battery point,

and also wire to the red probe of the multimeter. Using another piece of wire, connect the

negative battery terminal to the black meter probe. With meter on 20V DC range, you

should see around 18-19 volts.

Now touch the black probe (with wire still attached) to the blade connector on the zener.

You should see the voltage drop down to 15 volts straight away. Don’t leave it there very

long – 2 or 3 seconds should be heaps. The internal resistance of the batteries will limit the

current, but the wires may still get warm or hot.

If it goes below 15 volts (eg 1 or 2), you either have the diode forward biased (reverse the

connections on the zener) or it’s faulty (perform the previous simple multimeter diode test).

If this is the case, the wires will get hot really quickly, and the batteries may also get very hot

if the probe is left on the Zener too long. This is why I’ve suggested to just touch the probe

on, and not wire it directly to the batteries – easier and quicker to remove.

If the voltage doesn’t come down from 18 to 15 volts, the Zener could be open circuit (check

your test connections, and do the simple diode test).

4.5 Alternator

Two basic types of alternator may be fitted to your bike; A single phase alternator, or a 3

phase alternator. It’s pretty simple to tell which you have. Take a look at the wires and

connectors coming out of the lead coming from the alternator. If you have two wires coming

from the alternator, you have a single phase system. If you have 3 wires coming from the

alternator, you have a 3 phase system. The 3 phase systems require a special 6-diode

rectifier pack, and puts out a slightly higher current than the single phase system.

The two basic parameters affecting alternator performance are the strength of the rotor

magnet, and the speed of rotation of the rotor. The stronger the magnet, the greater the

voltage developed across the stator windings, and therefore the greater the current

capability. Maximum output current for a standard single phase alternator in new condition

is approximately 9 amps. Magnets will lose some of their magnetism over time, because of

mechanical shock and heat, thus reducing the output capability.

The windings of the stator do not usually degrade in terms of performance, but can be

affected by knocks during maintenance, or shorted turns due to insulation breakdown over

an extended time. Output can also be reduced by frayed connections, where not all of the

conductors in a wire are connected, and thus current-carrying capability is reduced.

4.6 Testing the Alternator stator

There are two fairly simple tests for the alternator stator, both done with a multimeter.

Disconnect the cables coming out of the alternator, where they connect into the loom. Note

which wires goes where before you pull them apart.


Now with the multimeter on the lowest resistance range (200 Ω), test the continuity

between the two wires coming from the alternator – you should see around 1Ω or less. If

more, you have a faulty wire or connector in the lead coming from the alternator, or a faulty

stator (rare but possible).

Now check the insulation from the stator to earth. Multimeter on highest resistance range

(eg 20M Ω), and measure between one of the alternator wires and earth, should read

infinite (“1” then blank on the meter). Do not have your fingers on any probe metal parts, as

this will give a false reading. If not infinite resistance, the stator could have a short to earth

via the metal core, or the cable could be broken and touching the engine casing.

Check the state of the connectors and the wires between all components, especially

between alternator stator and rectifier. Frayed wires at the connectors limit the current

capability of the wire, as all the wires don’t make good contact. This can make the charging

system operate below its full capacity.

4.7 Battery

The standard battery for the older triumphs is of the lead/acid variety, with a rating of 12

volts and 8-9 amp/hours. Some owners prefer to replace the lead/acid type with Absorbed

Glass Mat (AGM) maintenance free type. They still contain acid, but have no drainage tube,

are less susceptible to the affects of vibration, and have the same charging characteristics as

the standard lead/acid batteries. They are smaller in size for the same amp/hour capacity, so

fitting may present some issues (eg. Battery movement in the battery carrier cradle). Gel Cell

batteries are not really suitable for these bikes, as significant modification to the charging

system is required to limit the charge current to the battery. Fitting a Gel Cell to a bike with

a standard charging system will significantly shorten the life of the Gel Cell.

There are several tests that can be done on the battery, such as specific gravity of the

electrolyte (liquid) with a hydrometer, fluid level, standing voltage, etc. but by far the most

effective test that can be simply achieved is the “voltage under load” test.

To do this test, first connect the multimeter on 20V range directly across the battery, and

read the voltage with ignition off and all lights off. A fully charged battery will read pretty

close to 12.8V. A 50% charged battery will read 12.2V with no load, and a discharged

battery will read 11.9V with no load. Make sure the battery is fully charged before doing

the load test. Motorcycle batteries should be charged at a rate of no more than 1 amp. High

charge-rate car battery chargers are not suitable for motorcycle batteries, as their charge

rate can be as high as 10-12 amps – this level of charge will boil the motorcycle battery.

Now turn the headlight on low beam. This will draw approximately 4 amps out of the

battery. The battery voltage will drop to about 12.2 volts as soon as you turn the headlight

on. Keep an eye on the voltage reading for a full 3 minutes. If it falls below 10 Volts, your

battery is faulty, and needs to be replaced. If the voltage drops to 11 volts, the battery is

weak, and you need to consider refurbishment or replacement. A good battery will read

around 11.9 to 12.2 volts after 3 minutes. Switch the headlight off, and after two minutes

check the reading again. That battery voltage should have crept back up to around 12.6 to

12.7 volts. If so, your battery is in good condition.


4.8 End-to-end Charging system testing

If you are satisfied that all the charging system components are in good condition, you then

need to check the overall system operation.

The two basic checks to do for end-to-end testing the charging system are:

• Check the battery voltage with the engine running around 2000 rpm – should read

around 13.7 to 14.2 volts. If down at 12 volts, you have a problem with one or more

of the charging system components, or cabling/connections between them.

• In a shaded area, locate the bike near a wall or similar, so the headlight will shine on

the wall and you can readily see the light pattern. With engine running at idle, turn

the headlight on high beam. Engine revs may drop a little (good, because the

alternator is loading the engine). Rev the engine to 2000 rpm, and the headlight

should get slightly brighter when the revs are up. This indicates that the alternator

and rectifier are working. Lower the revs and the light should go slightly dimmer. If

the light does not go brighter with revs above idle, perform the previous test for

battery voltage at revs.

5. Indicators

The wiring for indicators is basically as illustrated in Diagram 7. Note that the return current

path is via the ground/earth mounting of the indicator arms. Some after-market indicators

do not make good earth contact at the mounting points, and may require star lock washers,

or special extra wiring, to ensure a good earth.

The indicator system is made up of four basic components; the indicator switch, the flasher

unit (aka flasher can), the indicator lights themselves, and the indicator warning lamp.

Battery

Fuse

Ign Sw

DIAGRAM 7

Left Hand

Side

Right Hand

Side

Indicator Switch (handlebar)

Flasher Can

Warning lamp


The flasher unit, or flasher can, consists of two metal strips, one being plain metal with a

contact at the end, and the other being two strips of dissimilar metals bonded together,

again with a contact at the end. The bi-metal strip is surrounded by a heating element.

When current passes through the heating element, through the contacts and along the plain

strip (Diagram 8a), the bimetal strip is heated and bends (due to the different rates of

expansion of the two dissimilar metals) (Diagram 8b). This breaks the contacts apart, current

stops flowing, the heater elements no longer heats, and the bi-metal strip returns to it’s

original position (a). The contacts make, current flows, heater heats, bi-metal strip bends,

contacts break (b), and the cycle continues until current is stopped externally (switched off).

This simple heat-based on/off switching method also allows you to see when an indicator

main (front or rear) globe is blown by the quicker flash rate with a lower load. With one

globe open circuit, there will only be half the current flowing. The heater heats the bi-metal

strip to half the extent, the bi-metal strip bends to the point of just opening the contacts,

and the bi-metal strip takes less time to straighten up again after the current is broken by

the contacts opening. Similarly, if your battery voltage is low, the heater takes a long time to

heat the bi-metal strip, and the indicator lamps will stay on longer, and will have a shorter

off time.

The indicator warning lamp (in the headlamp nacelle) works on the principle of a high

resistance vs low resistance voltage divider. When 12V is applied to one side of the indicator

system, and the lights on that side are on, 12V is also applied to one side of the warning

lamp. The other side of the warning lamp is connected to earth via the filaments in the other

side indicators. With it’s low wattage and therefore higher resistance, the main voltage is

dropped across the warning lamp. A small amount of current actually flows though the other

side filaments, but no enough to make them glow.

6. Lighting System

The lighting system is again fairly simple. The battery and charging system in combination

are the source of current for the lighting system, and earth returns via the frame are

common, although the main lamps have their own earth wire.

DIAGRAM 8

a) rest b) activated


The lighting switch will normally have 3 positions – Off, Parking Lamps (aka Safety Lighting),

and Main. The headlight beam also has a control switch mounted on the handlebar,

switching between low and high beam.

There are two possible ways to have the lighting power routed. One is straight from the

battery via the fuse, and the other is to have the lights only available when the ignition

switch is on. Both have pro’s and con’s, and it’s really up to the individual owner as to which

way works best for them.

6.1 Faults in the lighting system

The majority of faults in the lighting system are either globes blowing (filament going open

circuit), or bad connections.

Globes blowing will usually be caused by:

• poor quality globes being affected by vibration

• excessive vibration through worn or brittle mountings

• excessive voltage (open circuit or disconnected Zener)

• filament age – if they built them to last forever, you’d never buy any more…

Bad connections can be caused by:

• vibration – connectors coming apart

• Cable movement – broken conductors inside the insulation due to constant bending

• Corrosion – due to age, or connections being exposed to the weather or corrosive

elements (eg battery acid, fuel vapour, cleaning agents, etc)

• Poor earth connections due to attachment to frame with paintwork.

The fault finding routine for the lighting system is as follows:

If all lights don’t work:

1. Check fuse and battery are in good condition. Check the fuse with a multimeter on

low resistance range. Even though it might look OK, it may be broken near an end

under the cap.

2. Fault is likely to be the lighting switch or a bad connection to or from it. If lights are

wired only to come on with the ignition switch on, check the ignition switch as well.

If it’s an individual light (not all of them) that’s not working:

3. Check the globe. Either testing it in another known-good socket, or testing it with

the multimeter on resistance range. Sometimes you can see the filament flopping

around inside the glass, or grey/black stains on the inside of the glass, signifying the

filament is blown. White stains on the inside of the globe signify that air has gotten

inside the globe, and the filament has blown and burnt the oxygen.

4. If the globe is not the problem, check the earth connection for the socket. With the

fuse out, check for continuity between the earth side of the socket and battery

earth. Multimeter on low resistance range (200 Ω ). If less than 1 or 2 ohms, move to

next step. If more than 1 or 2 ohms, start checking the cabling, connectors, and any

earth attachment points backwards towards the battery from the socket.

5. If globe and earth are OK, put the fuse back in and, with multimeter on 20V range,

start checking the power through the cabling and switches. A good place to start is

inside the headlamp shell (most lighting power routes through this area. Check the


connectors on the back of the lighting switch for 12V from the battery, then work

your way forward to the socket that doesn’t work.

7. Horn

The horn is a fairly simple electro-mechanical device that uses a switched electromagnet to

vibrate a plate, creating sound waves.

Diagram 9 depicts a simple horn construction.

When power is first applied (you press the horn button), the electromagnet energises, and

draws the steel vibrating plate towards it’s core. This causes a rod mounted on the

underside of the vibrating plate to break the electrical contacts apart, and current stops

flowing through the electromagnet. The steel vibrating plate snaps back to it’s rest position,

and the electrical contact meet and again allow current to flow through the electromagnet.

This cycle continues until the current is switched off externally (ie you stop pressing the horn

button). The vibration of the plate is at such a frequency as to create sound waves.

Most horns have an adjustment screw on the rear of the case to adjust the tone of the horn.

This screw merely adjusts the position of the upper contact, thus changing the amount of

movement of the vibrating plate required to make/break the contact.

7.1 Fault finding a horn

The horn is most likely to break down due to three causes:

• Internal corrosion due to exposure to the weather – usually caused by the

breakdown of sealing materials around the case and vibrating plate.

• Maladjustment or misalignment of the contacts, due to the adjustment screw

moving with vibration.

• Broken cabling and poor connections to the horn and horn switch.

To test the horn, take the wires off the horn connectors (note which way they go), and using

a multimeter on resistance range, check for resistance between the two connectors on the

horn casing. You should see around 16 or 20 Ω . If infinite resistance, you can try rotating

the adjustment screw on the back of the casing until you get a reading. Most likely you’ll

need to take it apart. Take note of which way the plate and the case are oriented together –

a couple of dots of liquid paper can help align when putting it back together. Take the plate

Vibrating plate

Electromagnet

Contacts

Casing

DIAGRAM 9


off, and check the internal connection and contacts, as well as the position of the

adjustment screw. Remember to seal the case against the weather – if a gasket is not

available, use a thin bead of silicon.

Remember, you should have a low resistance reading when the horn is not operating. If the

adjustment screw is adjusted correctly, you should be able to press on the vibrating plate by

using fingers, and cause the contacts to break the connection, making the meter read

infinite resistance. Let the plate go, and the reading should return to low resistance.

Connect up the power and earth cables, and test. Then adjust the screw to give the tone you

require. Be aware that the more the plate has to move (the lower the tone), the more

average power will be required to operate the horn.

If, when you connect it all back up and press the horn button, you just hear a click when you

press the horn button, and another when you let it go, the adjustment screw is maladjusted,

and the vibrating plate is not breaking the contacts.

8. A Few Tips

If your motorcycle electrical system is constantly blowing fuses, and you’re having trouble

tracing the fault, wire in a 20 Watt globe in place of the fuse. When a short is present

somewhere in the electrical system, the globe will light up. Start disconnecting components

one-by-one (eg rectifier, zener, coils, etc) until the globe stops glowing, and you’ve found the

faulty area.

The tube-type connectors used to connect the male bullet connectors together are

notorious for poor connections. Corrosion and broken metal inside the plastic covers are

common.

Frayed wires have less conductors to carry current, and therefore add resistance to any

circuit, which results in reduced performance. Fix or replace any frayed wires, especially

near connectors, and in high-current circuits such as charging and lighting. Wires that have

worn insulation may cause shorts, or allow moisture into the conductors, causing corrosion.

Repair or replace wires with worn or missing insulation. Heatshrink tubing can be handy in

these situations.

If the battery moves around in the holder, there’s a possibility of shorts to the seat pan, or to

the buckle on the hold-down strap from the active battery terminal. High density foam will

secure the battery in the holder, but make sure you don’t block the air intakes behind the

side covers.

Halogen headlamps provide better lighting, but also generate more heat. Be wary of melted

wires behind the halogen lamp connector in the headlamp shell.

Brake light globes have a tendency, due to the mounting rubbers, to wobble about a bit. This

causes either filaments to fail, or the glass to break on surrounding metalwork (eg reflector

mounting bolt). If you place a small dob of silicon between the globe and the reflector, it will

stop the globe vibrating, and prolong the life of the globe.

When working on the electrical system, have a blown-up photocopy (A3 size) of the

schematic handy, so you can mark off what’s been checked, and note voltages and other

readings at certain points.


Whenever electrical wires pass through metal, they should have a grommet or similar

protective covering around the metal edges, to stop the plastic covering on the wires being

worn away and the wire shorting to earth.

Some owners install a second fuse between the positive terminal of the battery and

frame/earth. While this can protect the battery and the loom in cases where the negative

terminal shorts to earth, it also adds another component that can break down and leave you

stranded. Always carry extra fuses, taped to the wires near the battery or to the fuse-holder

itself.

P.S.

Hopefully this information will help someone to keep their Triumph running and safe. Please

feel free to use it as a guide, but remember many of the older bikes have gone through

many owners, and thus may be fitted with many different components.

If you have any comments or suggestions for future versions, please drop me a line using the

TriumphRat.net PM system.

Pete.

electrical systems on meriden triumphs v3.0

Documents