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:
No power to the white wire. (Battery voltage low, less than 8 volts).
No earth to red wire.
Poor connectors. Tinning gone black or very corroded.
Coils or link wire open circuit.
Black coil wire shorting to earth + (Black box very hot).
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 removing unit and look around
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.
Boyer fitting instructions ( 249 kb )
Updated 22:59 2004-02-08
© Rickard Nebrér