My car has been sitting for 15 years. As you may guess, major electrical issues. I got the headlights working and some other stuff, but the dashboard is still not working. The voltmeter and oil pressure gauge are working. Tachometer, gas and coolant do not move. Any good ideas where to look? I checked the main fuse box on left blower and it seems fine.

 

If everything else is working, I would suspect the panel light rheostat. It could have built up corrosion after all those years. I would rotate the switch back and forth about 20 times (in darkened conditions) to see if you get any flicker of light from the panel.

 

Light rheostat affects tachometer, gas and coolant gauges? I would think its failure would leave dashboard dark and that's it?

 

Sorry Segfault, I misread and thought you were talking about the lights. I was thinking back to my own problems with dash lights.

 

I'd begin by pulling the cluster (easy) and carefully cleaning all the electrical contact points of the flexible printed circuit. Don't forget to clean the two harness plugs and add a redundant ground while you're at it.

Problems with the PC are so common I'm tempted to say that, by now, every old XJS has had this ritual done or needs it to be done.

Cheers
DD

 

Thanks, simple cleaning didn't do it. I think I will remove the PC and spend some time cleaning it.

 

Hi Segfault

The Rheostat only affects the illumination inside the Dashboard 'Binnacle' where the Rheostat Knob can be Rotated to dim the illumination, or if turned all the way round can turn it off altogether

That's its only function (basically its a dimming switch) and doesn't do anything else, where in the event that it ever goes wrong then that is probably down to a bit of Corrosion, as once its been set in a position that the driver prefers

It seldom or ever gets rotated again, so in the event that the illumination decides to go out, twisting it round a few times in both directions should get it working again (But it doesn't go all the way round!) don't try that or you could break it off.

As has been already said, your problem is almost certainly caused by Corrosion on the Tangs of the Two Multiplugs, that plug into the Printed Circuit on the Back of the Instrument Binacle

And although taking the Binnacle out is a very easy little job, you need your 'Watchmakers Head' on and be extremely Careful that you don't damage the Printed Circuit, as you can't go and buy another one

It took me Two Hours to clean those plugs and get the Plugs Tangs looking all nice a Shiny, as the Binnacle is one of those things you don't want to keep disturbing, if you can possibly help it

You can see how I pulled the 'Binnacle' out on Page: 76 of my 'Cherry Blossom' restoration thread, which I had to do to Fix my Speedo, which suddenly stopped working but after cleaning those Multiplugs, I did get it working again

Here is a link to that Page: Taking Out The Speedo Binnacle

 

Thanks! I can handle fragile electronics no problem. I actually removed the PC and inspected and cleaned it. Same with multiplugs. I added an additional ground wire. No change whatsoever. Speedo is working, oil gauge and voltmeter are working. Tachometer, gas and coolant temp are not. The next step is to start checking all wiring that comes to multiplugs, methinks. This is a long story, but there were some attempts made without my authorization to fix this car. I think some monkey screwed something up. Makes it even harder to troubleshoot.

 

OK, now the temperature gauge is working. The gas seems to have a sensor issue, it must be stuck or maybe sunk - I wonder what it is made of, plastic? That leaves the tachometer. Digging into schematics ...

 

Success! There was a wire snapped under the hood. A piece of heatshrink tube and a little soldering and it is all working now! Still have to figure out why the handbrake light stays on. Maybe the cable is stuck or something.

 

The gas float is indeed made of plastic and through some strange and mysterious (to me) form of osmosis absorbs gasoline over the years despite the fact that is is sealed. I've never understood that but on every xjs I've pulled the fuel sender unit out of, it's like half full of gas.. I'd pull the sensor and operate the arm manually and see if the gas gauge responds.

Of course the beauty of this job is without a gauge you don't know how much gas is in there, and therefore don't know if the fuel level is below where the sending unit sits.. oh joy :-)