I needed to run a single cable through the bulkhead for a temp gauge. Simple job ..yes. Well actually , of course it was. However when I had finished, car wouldn't start. The solenoid was clicking but the starter motor would not turn at all.
Obviously (to me) I had disturbed a cable/connection somewhere. So I checked everything ...made no difference

Then I suspected the starter motor and was just about to take it out when I realised that I could short it out. This I did and it worked fine. I then took some advice and got a mallet and tapped(thumped) the solenoid while a colleague was operating the key this made the starter motor burst into life for short periods.
Conclusion, purely coincidentally the solenoid main contacts had decided that they didn't want to work any more. Don't know why
it was only 42 years old. 
It was nothing to do with any of the original job I had carried out. New solenoid and I am up and running again.
As per my heading
I don't like car electrics!!!