Hey guys, I'm the new owner of a '97 XK8, I absolutely love it but I have no brake lights including the third brake light. I have working cruise control, I do have the ABS module errors of no stability or traction control but it's my understanding that's a separate issue (obviously I could be wrong, and I plan to address it soon with the soldering fix and I have a new front/left wheel speed sensor on the way), but those are the only display errors I have, and I just replaced my brake light switch. My other lights all work, taillights, reverse lights, parking lights, license plate lights, headlights, turn signals. So I'm not entirely sure what to look at next. Any ideas?

Thanks so much!
Jon

 

Did you check that the bulbs aren’t burnt out?

 

Yes, all the bulbs look great.

 

In the earlier Gen X100 there’s a known fault on the rear bulb’s ground electrical connection. Search for threads for fix by just riveting a new ground wire to the rear bulb panel to a new earth

 

I did see the ground fix, but would that apply to the bad 3rd brake light? Or is that likely a separate issue?

 

You said you fixed the brake switch, so assuming you don’t have a cruise control error, it’s probably one of a number of neglected issues from previous owner.

Fix one one at a time and work through it ... what may end up to be a long list

 

Cool, I'll do the ground fix and report back!

 

The brake switch has 2 micro switchers 1 for cruise and 1 for brake. It sounds like the brake light side is bad. The way the brakes work is when the switch is activated power is sent to the body processor and the 2 lower brakes light up. The upper brake light on the boot receives power directly from the switch, no module involved.
Since you do not have upper or lower it most likely is no power from the switch.

 

It took a bit of digging in the computers but I found it. Here is a great "How To" for repair and testing.


Jag XK8 Brake Switch replacement.pdf

 

So I did the ground fix and no change. I'll test the old and then new switch next.

 

Other than the brake switch, the stop lamp relay (#5 in the trunk fusebox) is common to all three rear stop lamps. You might check it's seated properly, or swop it with the fog lamp relay (#1 in trunk fusebox).

For the sake of completeness, check also fuses #6 and #8 in the same location.

 

I swapped relays around with no change, and the fuses look good. I am looking at the attach relay diagram though, is it correct for the stop lamp relay?

 

That diagram is for the 98, but substantially the same as 97 other than Jaguar either swopped the accessory & ignition positive relays or JTIS is wrong. The stop lamp relay is in the same place: