Right, through process of elimination through continuance testing I deduced the wiring to the cold start solenoid was grounding somewhere. So I re-wired that with a new manual switch through the same fuse and disconnected the old wiring. I left everything else in place and it all seems to work now.
Plenty more to do: rear reading lights still donât work and neither do the ignition warning light and the high beam warning light. And of course the interior light switch doesnât dim. But these are far more difficult to access⌠so leave for now.
Only other thing still not working is oil pressure switch/gauge (not sure which is not working at this stage). I bought a new switch on Ebay where they stated it would fit my car, but it didnât, so need to return that and get a new one.
Thank you all for your help, I could not have done it without all your sage advice!
Paul