Hello all! This is my first post, so forgive me for any formatting errors or faux pas. I’m gonna post this here just in case any of y’all had a similar problem I did.
I’d been having a hell of a time with my XJS. I bought her about a month ago, after it had sat for ~13 years. Troubles to be expected.
The main issues were electrical. The engine would turn over, and the headlights worked, but that’s all I had. No windshield wipers, windows, AC, radio, break lights, nothing of the sort to be found. One rainy day I happened to turn on my windshield wipers (they didn’t start) and then hit the ignition. Lo and behold, for as long as I was cranking on the ignition, the windshield wipers were working!
So, I immediately ripped open the ignition housing, and doused it all in canned sensitive electrical cleaner. And immediate improvements. Everything I listed before works now.
So, TL;DR? Having unexplained electrical issues? Clean your ignition grounds.
I still haven’t gotten my blinkers to work though…
Hmmmm. I wonder if that approach would work with the nice-looking, very low mileage black '91 w. sunroof (didn’t know our XJSes even had one ) for sale right now on Ebay. Seems the seller admits several of the ancillary electricals are not working on his car. If not (i.e. spray cleaner won’t cure them), seems like maybe a lot of costly repairs in order for the future buyer.
btw, Bangher … you mentioned quite some time back that the issue Superblue has with her speedo needle “rapidly fluctuating” about 5 MPH or so sometimes when in the 40-50 MPH range is due, if I understand your post correctly, to some kind of dirt or moisture having gotten into the connection (electrical) ribbon going to the back of the instrument panel. So, if I took a can of electrical contact spray cleaner to it, should that clear it up, then? I assumed though that the ribbon is “sealed”, so I really don’t understand how the cleaner can get into it. ?
I had a similar issue with the indicators not working after the car had been laid up. Turned out to be the hazard light switch on the dash - operate it a few times and/or get some contact cleaner into it - that might solve the problem.
) for sale right now on Ebay. Seems the seller admits several of the ancillary electricals are not working on his car. If not (i.e. spray cleaner won’t cure them), seems like maybe a lot of costly repairs in order for the future buyer. 
I assumed though that the ribbon is “sealed”, so I really don’t understand how the cleaner can get into it. ?