Many thanks for your detailed instructions, Dave. I used circlip pliers to get the silly screws out, and being away from home, sawed some slots in them and re-used them. Sorry I can't help with the wiring, but I guess you've either found out or lost interest by now. My problem was the switch, so I didn't push my luck with delving further! Couldn't see any way of getting the switch apart, and it worked intermittently. It improved with a dose of WD40, so I'm hoping for the best.
Roger, July 2019