Jaguar Repair: Inoperable Jaguar Fuel Gauge, fuel gauge, quarter tank

Question
QUESTION: Hi, I have a 73 Jag-XJ6 & the fuel gauge does not work. It stopped at a quarter tank although the fuel level is greater. Both of the sending units were replaced in both tanks about a year ago & the gauge worked at that time. Any pointers on easy troubleshooting. Thanks

ANSWER: Hi Bill,
You do need to remove the sending unit on which ever tank is reading wrong to be sure it is not stuck and not moving. With the sending unit out and something to cover the fuel tank hole, connect the wires up and operate the sending unit to see that it moves full scale. If both are not operating it is more likely the gauge. A rough test of the gauge is to turn on the ignition and disconnect the sending unit wire with the ground wire attached and watch the gauge and it should deflect the needle all the way and then ground the wire and the needle should deflect all the way in the opposite direction. If you gauge has the reserve light you will need to isolate that wire so as not to test the wrong wire. Sorry, I don't have a diagram of that car to tell you the color codes.
Howard

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QUESTION: I failed to mentioned that both my fuel & temperture gauges seem to have stopped at the same time on my 73 Jag-XJ6. Any pointers on troubleshooting the temperture gauge. I read somewhere that a bad voltage stabilizer could be the problem. Thanks

Answer
Bill, check both gauges for power as most gauges are powered from the same power supply. I don't have a diagram of that year XJ-6 but that is how Lucas does it most of the time. I don't know if they used a voltage stabilizer on that year Jag but they didn't on the later models that I do have diagrams of. Checking for power will tell you that anyway.
Howard