Chasing Electrical Gremlins in the Dash. (Aust XJ6 III 4.2l)


I am having issues with why radio, temperature gauge and speedo all going dead …

The temperature gauge has only just started to randomly fail. The sensor is good.

Funny thing is that they are all randomly dying independent of each other.

Can anybody give me some direction on what to look for?


Australian XJ6 III 4.2

The other instruments and instrument lights are working as they should, Tom…

There is no common denominator between these three items only - and three separate faults are possible. And intermittent faults must be tackled with the fault present…

Grounding the temp gauge connector at the sensor should peak the gauge - no reading implies power loss, or a faulty gauge…

Have you checked the in-line radio fuse? The radio has separate feed for ‘standby’ and ‘on’. Does it retain memory - does the electric antenna (if fitted) work? Ground fault or simply defective radio?

Speedo (if electronic) is driven by the transducer on the gearbox. Do you have the trip computer?

xj6 85 Sov Europe (UK/N)

Failed dirty grounds and/or bad cables/connections.

To add to what Aristides said, if your radio isn’t original and an aftermarket radio has been installed, check the wiring. I have seen radio rewiring for aftermarket radios with cut wires merely twisted together and taped. The cut wires should be soldered together and shrink tubing covered in my opinion but I know that crimp connectors are commonly used for speed. Some prior owner/shop crimped connectors have failed on my Jaguars.

I’d say you have three different independent failures, probably due to wiring issues.


Agreed…If the car has been in damp or moist climate, grounding and volt drops along with non use create these conditions.
Radio is a stand alone.
Speedo and tach are stand alone…
Pull the wire feed to speedo or push back on tight.
Temp is alone but heat to wire or corrosion on the sending unit side gets crusty as well.
You might be just draining down!

DITTO . Just was there. Some very odd behavior resolved by an added ground cable!!


Crimp or solder.

I see either as good, if properly done. if not well done, each is prone to fail.

I prefer solder and shrink tubing.

The worst is the “pinch”. An awful device that seeks to penetrate the insulation and latch in place…

Another is the mish mash connector fort battery cable to sub for a failed original., A means of clamping the frayed end of a cable with two small screws.

I’ve an original fire wall post to starter cable with a failed end. One of those junky ones might make it useful elsewhere. Not going to happen… A proper end, perhaps,. but, I was not impressed when I swapped in one from NAPA. Much better quality…

And, low on my list of connectors are the ones on my Jaguar’s side post battery…Ugh…



When I can I do both, solder and then also crimp and shrink tube. The best of both worlds !

Hi Tommo,
Sounds like what happened to me. turned out to be bad pin contacts in the harness plugs. I pulled them all apart and sprayed therewith contact cleaner all good now