Convertible quarter windows inop
 

I recently purchased a 1992 XJS V-12 Convertible and the quarter windows refuse to work. I have checked all the relays, the thermal breakers and replaced the hood control module. Still nothing. When I bought the car they were able to get the windows up and down by jumping them. I could simply install window switches but I’d rather have the system work as designed. I have checked the 30 amp fuse also. Holding the switch until the motor stops doesn’t help. The hood does go up and down as it is supposed to. Any help would be much appreciated.

Bumped it for ya.

How did you check the relays? I have put in functioning ( but used) relays that would click over when tested, but couldn't carry enough current for the window motor to operate. If the relays are original, replace then with 40 amp ( standard auto relays are 30 amp).

For the quarter rear windows to function (in a convertible), the parking brake is the key. When lowering the top, the parking brake has to be engaged. When raising the top back in place, the parking brake has to be engaged. The windows will not function without the parking brake set. I owned a 94 XJS convertible. Experienced the same issue.

Tibbetts,

As you say that the hood is operating correctly, then the problem doesn't lie with the handbrake switch. The problem must lie in the relays, window motors, wiring to the motors or (unlikely) the hood ecu.

Are you checking the relays by reading voltage output when the hoos is being lowered? (Easier to test on the down cycle because of the time delay from the ecu on the Up cycle.) If not, then backprobe the output wire from the relay when the hood down switch is pressed. If you're reading voltage at that time, the problem must lie in the wiring to the motors or the motors themselves. You mentioned that the motors can be powered directly so that points to the wiring, if you've tested the relays correctly?

So, if you've got output voltage on the relays when the switch is pressed, remove the 1/4 trim panels and see if you're then getting voltage at the motor. If none there, it confirms the wiring problem.

Good luck

Paul

The parking brake has been set. The hood goes up and down but no window movement. If the hood works, I think that means that the parking brake circuit it functioning. Am I not right?

I did some relay testing with a volt/ohm meter although I’m not convinced that my testing was conclusive. They did all click and each seemed to function properly when used in the hood up and down positions. It does seem like a relay related problem but it seems unlikely for all four window relays to fail.

This does sound to me like a relay related problem. I will get 6 new relays in 40amp if I can find them. I know Moss Motors stock the originals.

Yes, you are correct. I would follow Paul's suggestion above to check for voltage at the relays.

If the top/windows have not be used often, it has been reported that the motors can get 'stuck' and there isn't enough current to get them going. However, when I've experienced that, it was one motor at a time. So I would focus making sure current is reaching the motors first.

Good luck

Thank you so much, Paul. I have tested the relays to the best of my limited abilities. This seems like a relay related problem since the hood operates normally. Is there more electrical load on the window relays than the hood motor? It may be easiest to eliminate one possibility by replacing all relays. Hopefully before this drives me nuts.

For these cars, I wouldn't recommend throwing parts at a problem as that can get a bit pricey. If you want the most straightforward step, have you tried swapping the window up relays with window down relays and cleaned the contacts? It's highly unlikely you have four failed relays.

Next, I would remove one of your side trim panels and see if you are getting voltage at the motor. If you are, and you have a safe way of measuring current/amps I would then test that and see how much current is passing through the relay.

When I had a inoperable window, believe it or not, the fix was to tap on the motor while voltage was going to it. Viola! has worked fine every since. I also recall someone having those windows function once the side trim was removed and the weatherstrip was no longer putting pressure on the window.

Digikey is a good place for electronic parts. This one should work: https://www.digikey.com/product-deta...2161-ND/646987

The way the system is wired, going up, the current grounds through the down relay, and going down it grounds through the up relay. It grounds through the normally closed contact, and I have seen many relays that are dual rated: 30A for the normally open and 20A for the normally closed contacts. It grounds through the lower rated contacts and over time they burn and pit and can't conduct as much power as they should. I don't believe the hood circuit grounds through relays, but it's been a while since I looked at the circuit.

Thanks for your insight. I am digesting all the inputs. Everything points to faulty relays. What would be the reason that all relays seem to work on the hood motor but not on the windows?

I just ordered 6. This should eliminate the possibility of bad relays. The 40 amp. should be an improvement. Thank you so much for your help.

Mine only work with a tap on the motors every now and then....They all seem to go down but when asked to go up, then the problem arises.

Thanks. When jumped, both windows go up and down smoothly. I am going to try replacing the relays.

Thanks again for your input. I ordered six new 40 amp relays and replaced the originals. No change. The hood goes up and down but no window movement either way. I have already replaced the hood control module with no results. I’m baffled.

Thank you Paul,
i have just replaced all six relays with no results. Top goes up and down but still no movement of the windows. They both worked when I bought the car but they had to be jumped. Unfortunately I didn’t see how they did it but I know the motors and regulators work properly. I’m stumped. I’d like to try getting the, to work but don’t know which two points to jump. Any help will be appreciated.
thanks,
Tibbetts

Attached is the circuit diagram for the 1992 convertible top. Since the top goes up and down, we know the switches are good. The power coming in through the thermal breakers is not fused. I would start by putting a probe into the relay socket on the black wire and then to a good ground on the body and make sure you have continuity. If that's good, then make a small jumper wire and bridge the relay socket terminals. For example, to make the right window go down you would join where the 30 and 87 pins of the relay go in, which is the green/brown wire and the green/red wire

Tibbetts,

As Mac Allan said, I would really avoid spending money on parts until you've proved that they are faulty. I would still go back and do the voltage checks that I suggested:

- Back-probe the relay socket and check that there is voltage on the output pin when the hood down switch is pressed. Remember that it times out so check the voltage as the switch is first being pressed.
- IF you've got voltage at that time, then remove the 1/4 trim panels and check for voltage at the motor when the hood down switch is pressed. If no voltage, then your problem lies in the wiring to the motor.

Let us know how you get on.

Cheers

Paul

I have installed new relays. No change. I’ve jumped #87 to #30. Still no change. Is there a way to bypass the ecu?
pete

That should have done it. The relays are controlled by the ECU, so by jumpering the power at the relay socket you have removed the ECU from the equation. With a multimeter, can you test from with the green/purple or green brown wires and see if you have 12V from there to any ground on the body?

Is this test done with 30 & 87 jumped?

No, if you look at the diagram we are checking that there is power coming into the relay socket for the relays to switch.

As a thought, when you jumped the one relay, were the others in place? For example, if we want the window to go down, the ground path is through the up relays, so that relay has to be in place for the circuit to be complete.

Great point. I can’t remember. Will try again and will have all other relays in place. This would be so much simpler if Jaguar haven’t felt the need to be clever. Two simple switches, like most other rear window have, would have been better. Thank you for your help. I’m slowly becomes enlightened.
Pete

I did notice that when operating hood, I had to have both relays plugged in. Hood would not operate, either way, without both in place but works perfectly then. Again, I’m confused. Since neither of the windows work at all I didn’t realize that all relays had to be in place to get the ground.
Pete