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I own a 1996 XJS 4.0L Convertible. The rear quarter window motors are activated via relays and are protected by a thermal breaker. The front window motors are activated directly from the switch and are protected by a plain ol' 30 amp fuse. Why the difference?
The reason I'm asking is that I'm doing some rewiring which will include smaller switches and relays for the front windows and am wondering if I should add the thermal breakers to the front circuit or if it would be ok with just the 30 amp fuse.
Pete,
I don't know XJS but XK windows retract automatically prior to top/roof/hood operation.
If true for XJS quarter windows, relays would be required.
Alternatively, motors draw healthy current, Wire gauge requirement increases with length.
Relays allow the use of smaller wire gauge and smaller switch contacts for the control portion of the circuit.
Hi Bill - Thanks for the reply.
On the XJS the rear quarter windows go down with the top and are activated via relays with protection from a thermal breaker. There is no separate switch to lower them.
The front windows work from a switch connected directly to the motor via a 30 amp fuse (no relays) and have no connection with the top up/down operation.
I understand the reason for having relays. I'm making a new skislope for the car which will have mini switches in place of the existing switches (among other things).
I will be using mini switches and will be adding relays to the front window circuit.
So my question is: Should I add thermal breakers (as on the rear quarters) to the front window circuit or would it be ok with just the 30 amp fuse?
And . . . why did Jaguar decide to use thermal breakers on the rear quarters and just a fuse on the front?
My guess: The additional expense was likely not justified at the time of initial (coupe?) design. Thermal breakers would have been quite costly as emerging technology.
The convertible requires more complex electrical engineering, and the designers more credibility. They could "require" thermals in their area of responsibility but changing the existing door design would have been verboten?
I've moved your question from General Tech Help to XJS forum. Comparisons with other Jaguar models may be misleading and members here with the same model will be able to help.
I suspect it was partly a safety / quality issue. With the front windows being activated individually via switches and in visual control from the operator, I suspect there's less risk of a problem. They tend to be operated one at a time and any obstruction would be obvious and the operator would just stop pressing the switch and protect the circuit.
With the rear windows being activated via a signal output from the ecu rather than via an individually-controlled, AND being triggered both at the same time, AND being generally out of sight to the driver, AND with a time-delay of 8 secs on the Up cycle, AND with the greater risk of catching on the roof (hence the 8s up delay), there's far more likelihood of a problem happening. So, thermal breakers seem like a good idea in that situation
I suspect it was partly a safety / quality issue. With the front windows being activated individually via switches and in visual control from the operator, I suspect there's less risk of a problem. They tend to be operated one at a time and any obstruction would be obvious and the operator would just stop pressing the switch and protect the circuit.
With the rear windows being activated via a signal output from the ecu rather than via an individually-controlled, AND being triggered both at the same time, AND being generally out of sight to the driver, AND with a time-delay of 8 secs on the Up cycle, AND with the greater risk of catching on the roof (hence the 8s up delay), there's far more likelihood of a problem happening. So, thermal breakers seem like a good idea in that situation
Will be good to hear what you decide.
Paul
That's a lot of "ANDs"!
I agree. I've decided to just keep the 30a fuse for the fronts. I think the thermals are unnecessary for that circuit.
Now I just need to figure out the best way to run the wires from the trunk to the ski slope area and where to mount the 4 new relays and decide what kind of switches I want to use and how to lay them out on the ski slope and whatever else I want to throw into the mix.
"just rambling a bit" Nothing wrong with a little Sunday afternoon ramble. "stupid expensive" . . . and the winner is . . . JagBits @ $94.68 !!! Craziness!!!!!! https://www.jagbits.com/product/DAC11334.html
And you don't even get a reset button.
Easily replaced by these from Amazon. 2 for $11.99 if you want to stay in the thermal arena.
Just as a matter of interest, why are you running wires from the trunk? I though your thread was about changing the switches and installing relays for the front windows?
I think I would mount the relays with a bracket in the knee-bolster section by the thermal breaker. I guess that would keep the wiring runs shorter and easier?
pete,
Just as a matter of interest, why are you running wires from the trunk? I though your thread was about changing the switches and installing relays for the front windows?
I think I would mount the relays with a bracket in the knee-bolster section by the thermal breaker. I guess that would keep the wiring runs shorter and easier?
Paul
Sorry, I guess I left out some details. I will also be adding a switch to manually operate the rear quarter windows so I can put them down without dropping the top or have them up along with the front windows with the top down. I'll also be adding a switch to raise and lower the antenna manually so it stays down when I'm listening to my MP3s.
I've often thought about doing that. Obviously windows down with the top up is possible anyway, whereas windows up with the top down involves a switch from auto to manual which is always a bit fiddly having to get out of the car.
Just to mention, once you've done the mod, you might want to release the hood cover corner press buttons before operating the windows as I find that having the windows up can slightly strain the cover unless you've undone the corner buttons first and then re-attached them.
I have a 90 convertible and I had continuous problems with the rear quarter window motors. There have been numerous threads here and in the Jag-Lovers forum. Some suggested that the quarter motors overdrive and get stuck. One person installed limit switches and I bought some but couldn't figure out how to implement them. I had the motors apart numerous times and they worked on the bench but failed in the car. I tried getting a used top ECM from Paul's Jaguars that they claimed worked, but didn't. Mine worked but it had a broken case. I know...blah blah....but there were others who suggested directly wiring the quarters, powering separate switches from the front window switches. I considered using the available up and down relays for each quarter motor, but finally opted to directly connect them to power drawn from the 2 front window switches. That has worked perfectly for me. I used heavier gauge wire (14) than was used between the motors and the relays and computer. (I believe 18 or 20 gauge). I also eliminated the ECM from operating the top and just used the relays for the top, powering the control circuits directly from the top switch. My only issue to date is the actual front window switches which remain flakey. I've had them apart and cleaned them, and they work for a while, but then fail when I need them the most. I've had to pull them apart in a parking lot just to get the windows closed in a sudden rain. The ones I bought for the quarters (installed on the back side of the console as others have done) work fine. I may go ahead and do what you're doing and replace the front ones as well, but that will require changing out the connectors too...not looking forward to that.
. ... finally opted to directly connect them to power drawn from the 2 front window switches.
That was my first thought but I wanted to get over the switch cleaning routine. I'm planning on using mini switched so the need for relays. I'll also be replacing the top up/down switch and adding one for the antenna so I'll have 5 matching switches located where the existing switches are. One switch will control both rears windows.
Lotta switches, but my suggestion would be to use separate switches for each window. I suggest this for 2 reasons: should one not work for some reason, you know immediately where the problem may be; it's convenient should you need to only lower or raise one. And 6 switches has a symmetry that 5 doesn't :-)
Lotta switches, but my suggestion would be to use separate switches for each window. I suggest this for 2 reasons: should one not work for some reason, you know immediately where the problem may be; it's convenient should you need to only lower or raise one. And 6 switches has a symmetry that 5 doesn't :-)
I thought about 1 vs 2 switches but I can't think of any time I'd want only one rear window up or down so decided on 1 switch and I don't think troubleshooting will be a problem. Also, I'm a pretty asymmetrical kinda guy. Here's my proposed layout. I haven't decided on what I want to do with the upper section. I just know the ashtrays are going and I don't want cup holders (the area is too small to be useful).
I see you're less than an hour north of me. Maybe get together to compare Jags someday?
I really like your layout, Pete. I pulled my ashtrays too with the intent of installing cupholders. I bought a couple from some marine outfit with a notch for a coffee cup handle, but they're just too big and you're right....there's not enough real estate. I'm trying to figure out what to do with the rectangular holes. I'm thinking small boxes for coins and such.
Yeah, we
are very close by each other. Be great to get together and compare vehicles. Here's a shot of my BRG in the garage....much prettier with the top down.
Eric
03-25-2022, 07:17 AM
Electrical Question
