Cheers Oddjob, Im going to see what else Ive got.
The thing that threw me was the thing works when grounded .
It looks to my non electrically trained mind that the solenoid gets power from the small black wire and the yellow/red is earthed when the switch is pushed, thereby creating a circuit.
My switch (550} has an extra wire from clutch lever switch (to stop in gear starting without clutch, I think) I reckon I could use this switch by making it earth and doing away with the black "safety" wire. Anyway what could possibly go wrong.
