Graham,

I have a Perkins M60 - same as a Volvo MD22 so in the same family as yours. I'm not sure the wiring is identical but I think it works on the same system of an isolated engine. I wonder have you got current at the solenoid or just know that it has voltage getting to it when you press the stop switch? Have you double checked the wiring including the earth relay in the stop solenoid curcuit for loose or corroded connections? Have you tested the solenoid directly bypassing the engine earth? Excuse me if you have already done all this but if you have, say, a loose or corroded wire on the earth relay you will have voltage at the solenoid but it not work because of an incomplete curcuit.

Regards
John Maramu #92