Back to Home Page........
Back to Catalogue
Simple Tests On the Boyer Bansden MkIII Ignition Units For British Motorcycles
1. Swithching 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:
a: No power to the white wire. (Battery voltage low, less than 8 volts)
b: No ground to red wire
c: Poor connectors. Tinning gone black or corroded
d: Coils or link wire open circuit
e: Black coil wire shorting to ground (black box very hot)
f: Coil connected to black wire shorting inside from primary winding to case
(very common on Norton machines) (black box very hot)
2. Wires can rub through to frame, check by romoving 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 on 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 ground, could be either coil)
If test No. 1 is correct but no spark is produced on swithcing 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.