So...when I bought my 1990 XJS convertible, the speedometer didn't work. As part of the initial fixing, we replaced the sending unit - my new best friend, the Jag mechanic, did say that might not be the whole issue, but let's see. For the short time I've driven her, that seemed to be the fix.

Until yesterday. The speedometer did not work in the morning, but did in the afternoon. I spoke with the mechanic who said basically, yeah, well, told you we had to start with the sending unit but....

Now it worked for a while, after a bang on the dash (love percussive maintenance!) but now seems to have ceased functioning again. Having to use a Jag mechanic for repairs is getting costly (just did the Crank Speed Sensors last week) so anyone have any thoughts on what it could be before I wince and hand over my credit card?

I'm probably going to ignore the problem for a while if I can, but not sure if that's going to be practical...

 

This sounds very likely to be poor electrical contacts in the instrument pack. There is a blue plastic circuit 'board' that carries the signal and the earth return and the plugs that contact this from the loom can often wear away the copper tracks.

The terminals themselves on the instruments where they join the blue circuit board get corroded etc etc. It is reasonably easy to remove the pack and clean it up, but is easier with the steering wheel off. If your mechanic has done it before not more than 2 hours start to finish including clean up. If a track is worn where the plug goes into the pack, a little sliver of alum foil will repair it, or some copper tape with electrically conductive adhesive.

Greg