For some time I could not get my Volvo TMD22A to stop using the key. Not a problem as there is a mechanical stop. An electrician finally traced the problem to the 55 amp grounding fuse which had blown. Fuse replaced problem solved.? Not quite...
I now have a much more serious issue where occasionally when one turns the start key there is no power at the start control panel and obviously the engine does not start. So far, this only seems to happen when the engine is hot after a long run. Leave it for half an hour to cool and power to the starter panel returns. I am about to replace both the start and stop resettable fuse relays in the black plastic electrical box on the front of the engine to see if that helps.
