Old Britts

Troubleshooting the Boyer Bransden MKIII Ignition Units for British Motorcycles

If Your bike has stopped, follow the following troubleshooting steps:

If there is no spark:

Run a wire from the negative side of the battery (remember. Norton is positive ground] to the white wire on the black box. This will bypass the Ignition and kill switches and associated wiring. Disconnect the white/black and yellow/black wires from their terminal at their stator unit in the points compartment. Touch them together, when you pull them apart, you should get a spark at both Plugs- If you do, the problem is in the wiring from the battery to the black box. Check the kill switch first (remember it winds through the headlight) or perhaps a terminal has come loose. If still no spark: Check the coils next. If you are running two or three coils, these are wired In series, so if one coil quits , they will all quit. Very common if you are running dual 12V coils. Otherwise, the black box her gone bad on you.

Common causes of no spark:

Simple Tests for the Boyer Bransden MKIII Ignition Units

1. Switching the ignition on should produce a steady current through the ignition coils except for the Norton unit. This remains off until triggered by turning the engine or disconnecting the yellow/black or white/black wires.

No current through the coils could be caused by:

2. Wires can rub through to frame, check by removing unit and look round all the transistor box wires.

3. All battery cells should be in good order as one poor cell will produce a high resistance supply to the ignition. This can make the ignition spark on switching lights or horn and in some cases may produce a continuous run of sparks.

4. Switching off ignition should produce a spark at all spark plugs. The Norton unit would require triggering by turning the engine or disconnecting yellow/black or white/black wires. (Firing on one cylinder only, one coil shorting to earth could be either coil).

If test No. 1 is correct but no spark is produced on switching off, the transistor box is faulty.

5. The Transistor box can be tested in circuit by disconnecting the yellow/black and white/black wires and with the ignition on they can be touched together and broken, this should produce a spark at the plugs. If not the box is faulty.

If your bike is hard to start and fouls plugs:


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