I discovered the bulb holder in the cigar lighter was acting up, slightest movement and the light went off...so it had nothing to do with the engine

and as it was a freebie from the scappy's many moons ago have bought another with a better design separate + & - feeds for the bulb.
The light switch I used contact cleaner and that fixed that.
You hear about the Veccy's and earthing problems, plus the sensor issues I have at mo... my mind was thinking they were related lol