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Jaguar Repair/1984 Jaguar XJ-S HE


QUESTION: My Jaguar's doors won't lock, and also the fuel gauge is not working at all. So I was wondering what I could do to fix mainly the fuel gauge. Thank you.

ANSWER: Hi Joseph,

Go to the fuel tank and remove the light green with the orange tracer wire and the black wire off of the sending unit and turn the key to "ON" not start. Then take the two wires and touch the two wires together just for a moment and watch the gauge. The needle should deflect all the way either to full or to empty then disconnect them and the needle should deflect all the way to the opposit direction. If it does this the most likely suspect is the sending unit.

If nothing happens at the gauge with the key on or off with the wires connected together then you need to check for power to all the gauges with the key on. (this is fuse #4 in the main fuse panel)

You can also test the low fuel light by removing the brown with a pink tracer wore on the sending unit and turn on the key and ground the wire while watching the low fuel warning light as it should light up when you ground the wire.

If you get nothing from either, you may have a disconnected plug in the harnes under the center consol.


---------- FOLLOW-UP ----------

QUESTION: So I tried the first part, nothing happened. I also looked at the fuses and they looked all good, I even replaced the fuse and that didn't help with anything. I had a buddy of mine help me, and he was wondering since I got the car from my neighbor who gave me a brand new Chevy V8 engine, and transmission also new, if that would affect anything? If you need to see any pictures tell me what to take a picture of and I can send them to you. Thank you for your help.

Ok, now that you know that connecting the two gauge wires together does not make the needle do anything (with the key on) now you need to start testing.

Just as amy Jaguar mechanic would need to do at this point. The tests are not difficult and only require a few tools. I will walk you through each test. If you don't have a 12 volt test light you can purchase one at any auto parts store or Radio Shack. You will also need a Volt / Ohm meter. You don't need an expensive one. (don't forget to get batteries for it) Both of these tools can be used on any brand of car and are not expensive.

Looking at a fuse is of no use. You need to test the fuse with the test light to see that both sides are hot (powered with the key on) This tells you that power is reaching the fuse and leaving the fuse.

The volt Ohm meter will have several ranges and settings. Set it on "DC" Volts and on a LOW Volt scale if it has options. Place the black lead on the black wire at the tank sending unit and the red lead on the Light Green w/orange tracer wire and turn the key to "ON" (not start).
If you see no voltage, remove the black test lead from the balck wire and put the balck test lead to a good ground. (a bolt head or clean metal) and if you still get no voltage you have to go to the fuel gauge and do the same tests at the light green w/orange tracer wire there. (key on) if you still get no voltage put the red test lead on the other post of the fuel gauge. (key on) Here you must see about 12 volts. If you still have no voltage go to the #4 fuse in the main panel (driver's side) and check for voltage on BOTH sides of the fuse.

That is a 100% test of the fuel gauge system and you can not fail to find the fault. Voltage goes from the battery to the ignition switch to Fuse #4 and from fuse #4 to the fuel gauge and from the fuel gauge to a connector under the consol and on to the fuel tank sending unit and through the tank sending unit to the black wire to the body and back to the negative post of the battery. By testing along that trail with a volt meter, you can find where the problem is.
Never toss money and parts at any car problem. Always test and find the problem and then you can toss money and parts at the known problem.

If you got a Chevy V-8 with the car just set the V-8 down next to the XJ-S. If the Jag has half a brain it will know that the Chevy V-8 is a common conversion and that will scare it into behaving. ha! (it is like a heart and brain transplant)

Let me know,


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Howard M. Fitzcharles III


Jaguar from the XK 120 to XJ-6 ser. 3 1987


Dealership line mechanic on MG, Triumph, Jaguar for 15 years, Instructor in commercial mechanics school 2 yr. Product information manager for piston and valve manufacture, Instructor & hotline answer man for import car parts importer 15 yrs.

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Import Car magazine

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