Hi there!
I have an '85 XJ6. Sadly, it gets driven only intermittently and sits outside year round. Not for lack of affection, just circumstances beyond my control.
After a seriously rainy month, I took it out for a drive. It ran fine, but I soon noticed that none of the gauges were working, including the speedometer and the tachometer. Also, the trip computer and the cruise control weren’t working either. I would guess that’s because the speedometer isn’t working. 
I checked a fuse or two by replacing them with new ones, even though my test light showed them to be good.
I’m guessing I’ve got a serious grounding issue caused by the wet weather. However, I’ve owned the car for eight years and we have had plenty of wet weather during that time and this issue has never arisen in the past.
I would appreciate some help. I don’t know where to start.
Thank you!
Michael
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You are probably right about lack of ground, Michael…
However, while some of the instruments are fitted to a metal sub-panel with its own ground wire for common electric ground - the speedo/tacho is grounded to the body. Bad contact here may be cleared by removing and refitting them. As may the other instruments - wet weather means rust, which certainly may interfere with connections…
While power feed may be a cause; instruments are fed from different sources - which doesn’t prevent loss of power, or indeed a combination of factors on individual instruments. Have you checked out if anything else has failed - it may provide a clue…?
Frank
xj6 85 Sov Europe (UK/NZ)
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Hi Frank!
Thank you for your response. I shall go “ground hunting” as soon as
the temperature around here drops down to 90F. It’s been in the mid
100s the past few days. Before that it was raining!
Michael
Quoting Frank Andersen via Jag-lovers Forums noreply@jag-lovers.com:
Sort of quick-check, Michael; disconnect the plug of the water temp sensor and check voltage. Voltage will indicate that at least that one has power, and that ground is not the problem - or vice versa.
Also; I ‘think’ instrument lighting shares ground with instrument functions - so if there is light there is ground…?
Frank
xj6 85 Sov Europe (UK/NZ)
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Hi Frank!
Thank you for the diagnostic tips. I confess that I haven’t worked on
the problem since I first reported it. Soon!!!
Michael
Quoting Frank Andersen via Jag-lovers Forums noreply@jag-lovers.com:
With any electrical problems like this where connections are disturbed, can I suggest an application of Deoxit before reconnection to reduce likelihood of future problems? Especially relevant for gauges etc where voltages and currents are low. In some climates an annual check of all ground connections is a good practice - disconnect, clean, abrade surfaces, Deoxit, reconnect. Also relevant for rarely moved items like relays and fuses - pull out, clean, Deoxit, replace.
jp
Hi John!
Thank you for your insight. However, I have given the car to a
neighbor’s son for him to deal with. I will pass on your
suggestions to him.
Thank you!
Michael
Quoting John Pitman via Jag-lovers Forums noreply@jag-lovers.com: