I have a 1991 Jaguar XJS convertible. Rear window malfunctions are common in the XJS convertible. A friend of mine had the same issue with his driver's side window and fixed it himself. He's an experienced restorer of classic cars and offered to help me with mine. We took my drivers side rear window apart and cleaned the motor and put it back together again. We mounted it back in the window well but before we put the cover panel on we tested it and both rear windows worked! We put the cover panel back on and now neither rear windows work. We tested relays and all relays are receiving power. We are completely stumped! Has anyone run into this problem? I know classic jags can be quirky but this is driving us crazy. It does not make any sense. We now think it may be the electrical "brain box" that isn't sending the signal to the windows correctly but we don't know how to test this. Does anyone have any suggestions? Do you think these problems are related or completely separate issues? Any suggestions on what to do? Thanks in advance for an advice you have!

 

Sherri,

When you put the motor back and both windows worked, how did you do this? Was it by operating the hood switch and thus using the ecu and relays? Or was it by applying power direct to the motors?

When you operate the hood down switch, is the hood ecu applying the signal to the relays for the rear windows?

I'm assuming that in all your testing the hood is going down when you operate the switch but the rear windows are not lowering? If so, it is unlikely (although possible!) that the ecu will apply the hood down signal but not the window down signal.

Start by looking for the ecu output signals. Once verified, work forward to ensure they are getting to the relays. Then work forward to check for output from relays. Then move forward to check for voltage being received at the motors.

Good luck

Paul

 

Sherri,

One other quick thought:

You mention that the windows are stuck down. A naive question, but you do know that there's an 8-second delay built-in before they will start to rise when the hood up switch is pressed?

Cheers

Paul

 

You are so right that the quarter windows are a problem. This has been discussed time and again in this forum and in the Jag-Lovers forum. My personal view is that Jaguar was too clever by half with the top computer black box and the 8-second delay. I've taken apart my quarter window motors multiple times, cleaned them, bench-tested them, and reinstalled them only to have one or both fail to respond to the computer. There have been multiple solutions recommended on these forums. One guy said that the motors were over-driving and put in stop limiters. I bought a couple but couldn't figure out how to mount them. Others have installed a separate switch to drive the quarter windows.

In my case, the top switch was almost as flakey as the quarter windows. My solution was to eliminate the top computer entirely. I installed 2 separate switches, one for each quarter window pulling power from the front window switches and directly driving the quarter window motors with 16 gauge wire...no relays at all. For the top, I wired the switch directly to the top-up and top-down relays. Everything now works without issue every time.

 

Paul,
Thanks so much for your advice! Yes I'm aware of the 8 second delay. My hood has operated flawlessly through all of this. (I hope I didn't just jinx it!) I'm using the hood operating button to raise and lower the hood. Next weekend we're going to try and trace and walk the current testing as you suggested in your first post. I live in Alexandria, VA. If we can't figure out the problem does anyone have a mechanic they can suggest that will work on this in northern Virginia? Thanks for your advice!

Sherri

 

Eric,

I hope it doesn't come to this, but thanks for the info! Good to know there's a work-around if I can't the the ECU and relays figured out.

Thanks!
Sherri

 

Good luck Sherri,

IME, the problems with the rear windows is almost always with the relays, wiring to motors or the motors themselves. Hence my suggestion of tracing the output from the ecu forward. The ecus don't tend to fail generally. If it is signalling the hood, then it generally also will be signalling the windows imo.

Cheers

Paul

 

You have three options. One is Top Line in Springfield. All they do is Jaguar. They have all the know how. They aren't quick and they're communication isn't very good either.

There's also Master Auto Jaguar. All they do is Jaguar as well. I prefer these guys to the latter... and Springfield is closer to me! They were able to find and solve a problem I had, which turned out to be a leaking intake manifold gasket. Top Line was not able to diagnose it correctly.

Both shops are knowledgeable on these cars, however any shop that specializes in older convertible cars should be able to sort this out for you. There's a british auto specialist in Merrifield, British Standard Motors. These guys might be best suited for this kind of manual labor hunting.... also not quick. They will chat you up for hours if you have the time.

 

I'm guessing it's almost 100% certain it's the relays. The way the system works ( at least on my 94) is there is power to go one way and the ground path is supplied by the other direction. So to go up, power goes through the up relay to the motor, and the ground path is through the down relay. The ground goes through the 87a terminal of the relay, and the power goes through the 87 terminal (relays have standard terminal numbering). The system reverses to go the other direction.

The problem is that auto relays generally don't have the same power rating on the ground terminal as they do on the power terminal, so a typical relay is 30 amps on the 87 terminal and 20 amps on the 87a. That lower rated contact is what usually fails on the ground path and the motor doesn't work.

Before you take it to a shop, I'd replace all the relays with ones that are rated at 40/30 amps instead of the typical 30/20. When I had this problem I installed half a dozen used relays I had on hand and none worked both directions. I put in new ones and everything worked. It's a cheap fix and easy to do. These are under $3 each and good quality:
https://www.digikey.ca/en/products/d...1-R-12V/646987