I didn't put my meter on it, but since it needs to be grounded to activate the relays, there must be voltage on the wire at all times. When I cut the wire the windows didn't work, and when I installed the diode backwards the windows didn't work (I originally assumed that I needed to put +12v on the wires so I accidentally installed the diodes backwards.)

 

Guess what I am really asking is if you forget to lower the rear windows when you raise the top back up, will you damage the seals or will the top get hung up on the raised windows?

 

Damn, you're demanding! At the risk of destroying my own car, I'll go back out to the garage and check it for you.

OK, I checked it. Here's what happens: The rear windows are canted inwards and the seal on the convertible top needs to pass through the space occupied by the top of the window in order for it to close. In other words, the top of the window presses on the center of the rubber seal rather than sliding past it as it does when you raise the window. As soon as I could see that the top wasn't going to clear the window I stopped the top and lowered the windows about 3 inches to give the top the clearance it needs. If I had just allowed the top to keep going, it probably would have either damaged the rubber seal, or broken the rear window.

So, if you can't remember to lower the windows before putting the top back up, maybe this mod isn't for you. I'm sure it would be possible to install a microswitch at the bottom of the window and run a pair of wires between the microswitch and the "Up" button. The microswitch would be open unless the window was down, and that would prevent you from raising the top.

Or, you could do something similar but instead of preventing the operation of the top, it would just activate a warning buzzer or something.

 

Sorry, I have been an engineering director for the last 20 years, sometimes I have trouble turning it off.

OK I think we found why this feature is not there from the factory. Let me think on it a while...maybe I can come up with a simple add on circuit to lower the window when the top is raised.

Oh, and how about a test drive so we can see how much improvement we get in noise and wind abatement

 

That's fantastic Sam!! It has always bugged me that these windows would not operate with the top down. Please tell us if you notice any difference while driving the car with the top down and all windows up. (and your windscreen down)

Thanks,
Greg

 

I could add a circuit that does that pretty easily. I just need a little time delay relay that will turn on for about 4 seconds when the "up" button is pressed. I'll see what I can do. Heck, maybe I'll package it as a whole kit and sell it. It couldn't cost more than $10 to $20. It all depends on how much the time delay relay costs.

 

That would work.

What I was thinking though would be more elegant is if you can utilize the timing of some of the relay or contact closures that are already in the system.

 

I confess, I haven't looked at any of the diagrams, so I could be wrong here, but do you actually need a separate switch to lower the rears when they have been manually raised? What I mean is could you just wire in a momentary button to raise the windows after the top has been lowered and then use the existing roof switch to lower the windows back down before the roof is raised (like the roof switch operates now to lower/raise the windows without lowering the roof)

 

Wow,

You guys are incredible!!! People come on here all day long asking questions. if it's something that has already been discussed, someone points you in the right direction immediately!!

If it's something that hasn't been tackled or solved yet, someone usually jumps right on out there to do the incredibly time consuming work to figure out a fix, then document the hell out of it and posts it right back up on the boards for all to benefit from!!!

Then you have a few others that are so incredibly dedicated to the mark that they VIDEO TAPE the entire fix!!!!!!

Just incredible...

And I THINK I agree with Keith, couldn't you just hit the roof down button first and allow the system to lower the windows and then push it back up to raise the roof ??

Just use the new switch to raise the windows and the roof system to lower them.

OR, when you hit the lowr roof switch, does the roof system 'know' that the roof is already down and no need to lower the windows???

Looking forward to the final solution!!!!

Thanks again guys for all of the help you give to the whole forum!!!

Rich

 

This makes sense from a human logical perspective, but we are dealing with a piece of dumb hardwired logic here. The car will only lower the windows at the beginning of a top down cycle...in other words the top must be up. If it senses that the top is already down, it will not lower the windows.

 

Here's the video:

YouTube - Adding a Switch to Control the Rear Windows on a Jaguar XK8

By the way, the issue is that the windows cannot be raised when the top is down. I wanted to be able to raise the windows because my wife has beautiful hair and I don't want it to get messed up. With the combination of wind deflector and raised rear windows she should be able to ride without a single hair getting out of place.

Oh yeah... one last thing. That third wire that goes to the middle of the switch needs to be grounded under a screw. There are 6 easily accessible screws or bolts right there in the tunnel under the arm rest.

 

By the way... I have 5 of those rocker switches left. If anyone wants a complete kit I'll sell the rocker switch plus all of the necessary wires and splices all assembled for $10 including shipping. That's a good deal. I'm not making money off of it, just trying to help people out. I'll leave the wire long enough to reach anywhere in the arm rest tray, but if you want to put the switch somewhere else let me know and I can leave the wires longer. I only have 5 switches, after that you'll have to source the parts yourself. The spade connectors and splices are easy to find at any auto parts store, but I had to order the switches from China. I thought for sure that Radio Shack would have a three position momentary rocker switch, but they didn't.

Just send me a PM if you're interested. I only take PayPal.

 

Sam has a super concept here. I think this is a worthwhile feature addition and a well done video.

I am absent minded however, and I know the day will come when I raise the top back up and forget to lower the window first. This looks like it might cause expensive damage.

With the addition of 2 inexpensive single pole automotive relays available from Autozone or Radio Shack, you can add circuitry to provide an auto-down function when the top is raised.

The way this works is that the relays perform a logical 'AND' on two signals
that only get activated TOGETHER in the time from when the top begins to lift to raise back up to the time the top latch is contacted. These two signals are the two valve solenoids on the convertible pump and their wires are are easily accessible at the pump on the right side of the trunk (see photo of wires at yellow connector). When both these relays are activated, a ground is provided to the same window down signal (Green/Blue wire) under the console that Sam's window switch is connected to. This one wire will need to be run between the console and the trunk.

So now when the top is raised, the quarter windows will automatically lower. Connections to the car wiirng can be made with the same type of wire taps Sam shows in his video.

(Disclaimer: I have not tested this yet, but I am pretty confident it will do the job).

 

That's pretty clever, WhiteXKR. That got me to thinking, I bet we could do that without having to run a wire to the trunk. Getting the wire from the arm rest tunnel to the trunk does not look easy. The BPM signals the front windows to drop by an inch or two. I bet we could use that same signal to drop the rear windows at the same time. I'm not quite sure if an inch or two would be enough, but I could always try .

 

That got me to thinking and looking at the schematic again. The convertible top switch itself simply provides a ground that could be used...that would be sweet, but that excludes closing the top from the key-switch...rats.

Your idea is interesting, but I think you still need to 'AND' any signal controlling the main windows with something that says the top is closing.

It is actually not that hard to run a wire through the rear firewall...ask h20boy...he and I do it all the time.

 

The thing that concerns me is what happens to the rear window down motor if you leave it energized for the whole cycle of the convertible top? Is it like the front windows where the motor stops running and you hear that little click?

 

It is not running the whole cycle, but it is a significant part of the cycle. I had the same concern it might stress the motor...not sure of the answer without experimenting. Normal activation time is 3 seconds...this would activate it for about 12 seconds.

Do you hear any click when you hold your new switch down for a while ?

 

There is not a click sound when I hold down the rear window switch

I just scoured the electrical guide looking for a "hard" wire that controls the windows. Apparently the window control is all done through the SCP bus, so to get a signal from anything that controls the front windows to anything that controls the rear windows I'll need to run wires from the front of the car to the rear of the car. It's kinda funny. You'd think that there would be some way to interconnect the front and rear windows, but there is just nothing that interconnects between the front and rear windows.

 

And what pisses me off is that I was PERFECTLY HAPPY with my solution until you came along! Now I'm obsessed with finding a way to idiot-proof my invention.

And no... I'm not calling you an idiot! LOL!