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Jaguar Repair/XJS Jaguar Electric windows


QUESTION: Hi Howard,

I have recently purchased a 1981 XJS  in near concourse condition but the electric windows do not work. I cannot find the circuit breakers above the fuse box as described in the book. Also there is a large grey barrel  type switch with a plunger on top attached to the side of the car just inside the driver side door with a black plastic box covering it. the switch sticks out the top ? Any help gratefully received and appreciated.


Paul C

ANSWER: Hi Paul,

The thermal circuit breaker (a rectangle box with two flat spade terminals) should be on the lower far right side of the relay panel to the right of the fuse panel and the window power relay is a round 4 pin relay behind that relay panel.

The power for the relay comes through the circuit breaker from a direct hot all the time brown wire to the circuit breaker and on to the relay as a brown w/blue tracer wire. The power for the trigger of the relay comes from the ignition switch in the #1 & #2 switch position by a white w/pink tracer wire. The electromagnet in the relay is grounded all the time by a black wire. And the output power from the relay is a brown w/blue tracer wire to both window switches.

The large box which you found with a reset button is an inertia switch that cuts off the fuel in case of a crash.


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

QUESTION: Thank you Howard

I appreciate your concise help. I am a cattle Veterinarian trying to be an auto electrician. Recipe for disaster I suspect! Just love English cars



ANSWER: Paul, You will evolve into an auto electrician and there is nothing you can do to stop it. As a Veterinarian you will soon recognize that you have a non-curable disorder called "Just love English Cars". The disorder starts out with the purchase and driving (and repairing) an old British car. The car then casts a spell on you and you start saying things like "Just love English Cars". Next symptom is when you start saying things like "That is not an oil spot under my car, it is my cat marking it's territory". Then you will befriend "Lucas" (Prince of darkness). And fully understand why the Lucas wires must not have the insulation damaged and tell others that it is because it lets the smoke out of the wires as Lucas wires are full of smoke and it is important to keep it in.

You may progress so far as to put bumper stickers on your car like "Don't follow too closely! I have Lucas brake lights"

You will start defending your car when people say "Why do you keep that car when you seem to have to work on it all the time" You will start saying things like. "My car is like an F-16 fighter plane, it requires many hours of maintenance for each hour of flight". You will soon believe that and the worst part is that you will start enjoying it.

How far can the disorder progress? I don't know, but I am in the advanced stages of it. I have a yard full of Jaguars and I just finished building an MG (Frankenstein version) I severed the parts of many kinds of cars and built my version of the MG. In the menu under "Project Car".

Maybe as a Veterinarian you will at some stage find a cure. I wish you luck, but if not let me know and I will try to ease the pain along the way.


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

QUESTION: Hi again Howard.

My 81 XJS electric windows do not work. According to the previous owner they always worked however when he was getting the car ready to ship he pushed the cigar lighter in and it blew the number 3 fuse.
When the car first arrived it had some electrical anomalies which were largely cured with the replacement of fuse number 3 and a few globes.
As far as I can tell this should be unrelated to the electric windows.
I disconected the very dodgy lighter and replaced the fuse. In the console, there is a black wire attached to the body near the gear lever by a screw ( Earth ? ) but the other end of the wire is loose with bare wire showing and connected to nothing.
Is the lighter circuit affecting the windows, are the loose wires related to the windows. I have taken the window switches apart and cleaned them.

Further, My car is plated 06/1981 and is an Australian delivery car. The Vin is SAJJNAEY3AC 104983 with engine number 8S 17333 LB  It has the wooden veneer dash and large chrome mirrors apparently the early hallmarks of a HE however accordiding to some tables I have seen this car was manufactured in 1980 and is an original fuel eating spec! Any thoughts as to which model this car is?

Thank you for you thoughts and time

Kind regards

Paul C

Coming from under the dash into the console from the left is another black wire with a male copper end which is also loose and plugs into nothing.

Hi Paul,

I found while working in Jaguar dealerships that it is mostly a waste of time trying to diagnose an electrical problem by symptoms or guessing which part may have failed. The ONLY method I found works is testing. And the testing must be done in a correct sequence.

I doubt that an Australian version has any different wiring then a US version and I see that the windows are a simple circuit. I usually start at the load (item that does not operate) and work my way toward the power supply (battery). Some circuits make it easier to start in the middle and thus you will know which direction to go with your tests. The wiring diagram is nothing more then a road map showing the path that the current travels to get to an item (window motors in your case)

If you want to got to an address anywhere on earth you need a map and it is exactly the same when you are trying to got to a failed circuit in your car.

The fuse you are talking about has nothing to do with the window circuit.

You know that you have no power going to your motors as it is unlikely that both motors would die at the same time. So you need to take a 12v test light and follow the road.

You had the switches out so you should have tested for power to the switches at that time. This is about the middle of the circuit so turn on the ignition switch and check for 12v power at the brown w/blue tracer wires on both window switches. If there is power then you know for sure the thermal breaker and the window relay are both good. If you don't power there, you know you have a failure back toward the power supply.

If you do have power on those wires then put the clip of the test light on the power supply and touch the black wire leaving the switch (with it disconnected from the switch) this confirms that the black wire is a good ground. Now remove the green w/blue wire and the Red w/ blue wires off of the switch. If they are in a formed plug as many are you will need to make a short jumper wire to do the test. You need to touch either wire to the power wire while you ground the other wire and note if that window moves. If it don't switch the two wire connections grounding the wire you just powered and making the other one hot. This tests the wiring to the motor and the motor itself.

With these tests you will know where to look for the problem. Let me know and I will give you the next test.


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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.

Associate member SAE EAA member

Import Car magazine

ASE Master Auto with L-1 certification up to 2000

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