Any progress? The wind has shifted direction and now I'm back to thinking about the failure of a seemingly unrelated fuse. Have you seen these two threads?:

https://www.jaguarforums.com/forum/s...ystery-219022/

https://www.jaguarforums.com/forum/s...llights-53056/


I work in electronics and must admit I don't fully understand how such oddball problems can be caused by some other fuse. Makes little sense to me, but I just have to go along with it. As long as I know to check for this potential problem, the exact "why" details are something of a moot point.

This thread seems very similar to your scenario, but unfortunately it was never resolved:

https://www.jaguarforums.com/forum/s...lights-239311/


Fortunately, that last thread does have a comprehensive list of fuses to check.


A couple of thoughts about fuses:

1) Make sure you are using a quality brand. You may encounter very low quality with some of the no-name specials that seem to be everywhere. A few years ago, I foolishly picked up a huge kit of spare fuses. First thing I noticed was the blade material was thinner than typical. They did not fit securely in the fuse panel sockets. I ended up tossing the whole kit, although I saved the cool plastic box, so it wasn't a total loss.

2) If a fuse heats up (regardless if it blows), it can transfer heat to the sockets in the fuse panel. The heat weakens the temper of the spring metal, and the grip is reduced. To test for this, take a fuse and cut it in half so it only has one prong. Test each side of the fuse socket for proper grip. Don't use a whole fuse, as you want to test each side individually.

 

So since you’re troubleshooting, you’ll likely want to stick with halogen bulbs and I agree, the Philips bulbs are the way to go.

However, if at some point you decide to go LED, LasFit is the only brand I’ve found which does not throw dash errors and works properly. (Except for the stop/tail lights; I’ve found no LED bulb which works properly there and I’ve tried them all)

 

@kr98664 I’m gonna dive back into it today. Like you, the anticipation of the results of the test light are killing me!! That work thing has been getting in the way.

 

@raphsp3aks

Bumpity bump a few months later. Was this issue ever resolved? We've got another forum member currently experiencing a similar issue. It would be very helpful if we knew what happened with your car.

 

Hi, ​​​@kr98664 !

No, I never did figure it out. The car doesn’t get too much drive time, but that stupid tail light makes no sense to me. I haven’t given up per se, but sometimes you have to walk away to build up enough enthusiasm to continue on. That’s where I ended up. I’m on the road at the moment, but will make an effort to get back into it when I return next week.

 

These cars have a switched ground system which is confusing if you are use to the old setup. So with this system all the circuits are continuously powered by 12 VDC. When the computer see's you apply the brakes or switch the turn signals on it sends a command to the REM (In the rear of the car) and that module then provides a ground path so the bulbs will turn on.

In the front there is a FEM or sometimes it's called GEM.
With your problem I would suspect a REM problem and that would be where I would start troubleshooting.
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@kr98664 It took forever to close this loop (no pun intended). I replaced the wire from the right (passenger) tail light from CA63-4 to CA68-4 from end to end and it appears to have fixed the problem. I did replace it prior to, but it was a splice and apparently my splice wasn’t in the part that was damaged. The damaged portion was closer to the REM, and the work to undo the loom to access the wire was a huge pain in the butt.

I have a functioning blinker and also a functioning high/center mounted brake light. Took a year of trouble shooting! What a PITA.

 

BTW, the switched ground thing is difficult to troubleshoot. My method was to have my son hit the brake pedal and from there I was able to see how the voltage shifts from one pin to the other.

To be honest, had I started trouble shooting with activating what I was trying to test in the first place all of this would have been much easier to diagnose. Literally the voltage shifts from one pin to the other. I found it to be very confusing. There has to be another way.

Switched ground? Why? Whyyyyy!?