Hello fellow Jag enthusiasts


A fortnight ago I drove 15 miles in my 1991 V12 XJS to my "local" swimming pool. It was seven in the morning so I didn't use windows. After the swim I got back in the car, started up the engine and then tried the driver side window - no response.
Tried the passenger side - no response. On the journey back I noticed this clicking sound - sounded more like "tonking" coming from under the glove box. I arrived home and after some research realized this was the thermal cut-out fuse. The noise occurs as soon as the ignition is switched on and starts immediately and occurs every 5 seconds or so ( whether you operate window switches or not) . The cigar lighter and mirrors all work but the windows are dead.

I took off both window switches from the ski slope and then turned the ignition on - no "tonking noise". Mmmm - fitted two new switches - "tonking" starts again. Fitted a new passenger side switch and tested with no driver side switch fitted - "tonking" starts,
Fitted a new driver side switch with no passenger side switch fitted - Bingo! The driver side windows worked and no "tonking noise".

Having narrowed it down to the passenger side I am not sure what to do next. The passenger switch is probably not the cause of the problem as I fitted a brand new one so the fault must lie downstream from the switch. Do I have to take off the passenger side door card? Has anyone had these symptoms before?

One possible clue to all this - I did take a left hand band faster than normal on that drive to the swimming pool - maybe that caused a wiring issue?

 

I’m not sure about the noise, but I’ve had intermittent responses from both of my window switches. The switch is the most likely culprit, they’re all crap. Take it apart and clean the contacts. They’re bare copper and oxidize fairly easily. Some fine sandpaper should have the switch back in business pretty quickly.

 

If the exact same switch you used successfully in the driver's side produces the fault in the passenger side, then it is a wiring fault. Nothing for it but to get the wiring diagram and do some continuity testing. I can post a diagram if you need it.

 

Do not sandpaper the contacts! That wears away the surface and whatever is there below oxidizes in days, so you'll be doing this weekly.

 

Thanks Greg - a diagram would be helpful. Mine is a pre-facelift model.

 

Attached.

FYI, this supplement is really worth buying if you are keeping the car.
https://www.ebay.com.au/itm/25651873...S7WBSH7G05XTEE
Beware earlier versions; this one is the one to have. Note it is called "Supplement to the repair operation manual" in these precise words in this precise order on the front. I has absolutely loads of stuff in it, is not too long, and covers all the normal electrical stuff that tends to need repairing.

 

Thanks for the electrical diagram - they suggest a few checks. It does seem to be a wiring issue because switching the right side switch to the left side causes the thermal cut out to switch on and when the right side switch is moved back to it's proper position on the right and the left side is just empty (no switch fitted) the thermal cut out noise vanishes and the right side windows work.

I think the thermal breaker is working because under certain conditions ( right switch fitted, left not) there is a working window but when I invert that configuration the noise starts which I think means the thermal breaker is doing its job - i.e. the circuit is overloaded. The pdf you attached suggests checking the the voltage at terminal C1 on the window relay when the ignition is switched off , then when the ignition is check the W1 and C2 terminals. I have a multimeter so I think I could do this but wouldn't both windows fail if the relay was at fault?

The pdf also says check the fuse and all connections ensuring the earth connections are clean and tight. I am not sure where the earth connections are but that seems worth doing. They also say check the thermal breaker by joining the two leads together. I think the breaker is OK because it only starts breaking the circuit (signified by the 4 second clicking noise interval) - however I am not sure so will give it a try.

The circuit seems to overload when the left window switch is plugged into its socket - it's not the switch itself so I will have to check elsewhere.

Thanks for your help on this - appreciated - I might buy the book too - do you think it's still valid for my 91 car as it covers 82-85?

 

Mostly, if your car is a pre facelift, in which case the wiring diagram may be incorrect.

I would remove the doorcard on the non-working window, disconnect the motor and see if the circuit still trips out, even if the wires to it are not connected to the motor. If not the motor is the mpst likely candidate to have failed. You can also test the circuit by connecting the motor wires to a test light ans see if the light works Ok and the circuit does not trip.

 

Danny,

As we know that your car is a 1991 but pre-facelift, then I suggest that the diagram below is the one for your car.

As you've verified that the RH circuit works, then I'd suggest that not only are the thermal breaker and relay intact, but also teh integrity of the actual earth points (because this diagram indicates that they are common for LH & RH circuits).

I wonder if you've got a break or arcing of a wire to earth through part of the car metalwork on the LH side causing the thermal breaker to trip / pulse? The most likely place would be somewhere where the wires move such as where they pass from the A-post into the door. I would start by physicall checking the wiring loom at that point. Then I'd check contiunuity from the LH switch to the motor, which will annoyingly necessitate you carefully removing the door card.

Good luck

Paul

 

Thanks for your thoughts Paul.

It does feel like I will have to take the door card off - that fills me with dread! Your theory (and Greg's) adds weight to it all happening when I took a fast bend on route to the swimming pool. The garage is too narrow to allow the doors to open fully. I will wait for a sunny day and try doing it on the drive.

Will let you know how I get on.

Steve

 

Steve
If you have not done it before, the main bit of removing the door card is the large sized pozi holding the armrest/door pull to the door. You have to carefully pull back the silver trim ring, which is not easy, and then you wil see the fixing underneath it. Then open the door, there is one screw about midway along the bottom edge. Then the two screws holding the courtesy switch plate; after which you can lever off the door card round its edges, popping out the fixings.
To finally remove the card, it needs a GOOD shove upwards, which dislodges the central fixing and the top along the door.
Have a friend handy to disconnect the puddle light wires before completely removing the card.