Ok, I think we can rule out a ground issue. I connected it to the ground braid as suggested, machine still has the problem. I will get my hands on a multimeter tomorrow and wil wait for further instructions.

Ah the joy of pinball machines.

Also just discovered there is a little grey piece missing from the top left ramp on the superharger.

Does anyone know if this piece is really needed so is it just asthetics. Ocasionally, the supercharger is also slow, any ideas?