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I have had a lower than usual voltmeter reading for a while now, but 14.2 volt output from the alternator and 13.9 volts at the fuse box while engine running. Now when I switched on the ignition today there is no reading on any of the instruments, checked the fuse, feed on both sides of the fuse (No 4) reversing lights also not working. The only thing I can think of is break in the cable behind the fuse box. I have had the instrument panel out to see if there is anything obvious out of order, everything looks good and the voltage readings from the two electrical connectors as:-
Vertical Pin number 13 - 12.9volts
Horizontal PIN numbers 5 and 9 - 12.9volts
Can anyone give me the pin numbers that should have power to them?

1983 V12 Coupe

No easy answer I'm sorry to say. The instrument cluster is well known to have poor connections, broken tracks and bad earths.

Download Kirby's book http://www.jag-lovers.org/xj-s/book/Jaguar.html which is a wealth of information on all things XJ-S related.

Odd the reversing lamps are affected, are you sure they were working before the instrument failure?

Go about the fault finding carefully and logically, just removing and replacing the instrument cluster can add even more faults.

Thank you for your reply. Just taken fuse (no 4) out and tested for voltage on the pins vertical connection no 13 and horizontal 5 and 9 with ignition on and there was voltage, therefore I’m thinking one of these pins should have had no voltage with fuse removed. Therefore tested all pins on both connectors again only the aforementioned had voltage, when I refitted the fuse and switched on and tested all pins again, pin number 3 on the horizontal connector now has voltage and the reversing lights are working. Will now give the fuse carrier a good clean and refit the instrument panel as long as the reversing lights are continuing to work. Thanks again poprivet for your reply.

Fuse holder sliders and the fuses' spades themselves do oxidise -- expect intermittent connections in this weather.

Interestingly (or not) the Mk IX uses 1¼" olde-style cartridge fuses inserted into a sprung double clip fuse holder.
All four of them They don't seem to oxidise.

Used extensively in Marconi Marine radio rooms' equipment.
Even with the salty sea air they lasted years

Thank you for your replies. All back together and working. Lesson learnt again, check and check again these glass fuse holder connections before jumping to the the wrong conclusion.

I'm pleased you have found a solution.

I came across this diagram which may be of use to others needing information or if the problem should come back.

A slight aside. I had a recent issue with a developing over time drop in voltage. In my case tracked down to the power terminal, the insulated one that passes through the bulkhead behind the fuse box. Can give you a nasty surprise if you are not expecting it.

Nick

I have a vague recollection that the fuse holders blocks have an issue where bad connections cause local heating. That softens the plastic allowing the holder to bend, further reducing the connection pressure. The cure is a new block, and electrical connection grease over the connectors. But it might be a problem with a different model ...