My extensive search for an explanation has yielded nothing.

My third brake light started flickering, went dim, went off, went dim again, came back to full brightness then went back to barely there dim.

I didn't see anyone else with a similar problem. I imagine if a fuse was an issue they'd simply be off. So do the LED strips go bad? I couldn't find anyway to take off the housing to check for some kind of bad connection. As I said, the fuse was my only other thought. I don't know if the LEDs go bad after 10 years and 75k miles.

The flickering and dim nature of the lights are really puzzling me.

I have an 05 Super V8.

 

Flickering like you describe usually means a bad connection somewhere in the circuit. Possibly in the LED strip itself. This has happened in the X type high levels and these are a sealed unit. I have not look at the diagrams for the X350 but I expect it to be similar. If you can find the earth point if it has one or the feed and return wires ( as a lot of cicuits are switched earth of this age of Jag.) Get the meter out and see where the power is going when illuminated.

 

The rear brake light assembly is easily removed by pulling it down from the overhead.

This is a required step for dropping the headliner for repairs to sunroof drains, etc.

If I recall correctly, there are two 'connections' to the rear brake light, the main connector is probably tape-wrapped and is a clip-together connector. The other is not seemingly designed to come apart (thought I had broken it!), which I believe is near the bulb/lucite component.

Is it possible either of these has come loose? Good news is that this should not take very long to check...please keep us posted.

Thanks-
Mag

 

For you internet diagnosticians, a little more info.

When I start the car from cold, the brake light works for the first one or two brake uses. After that, it might dim after that and then it cuts out.

It may return to life during a long drive for a press or two.

I tried pulling down the cover but it feels brittle and I am far too timid. I worry I will make things worse and break it.

 

My LED strip inside eventually stopped working altogether. See my repair thread here.
https://www.jaguarforums.com/forum/x...ht-fix-113173/
I think Jag wants like $90 for a new LED light. I Didn't think it was worth it for what it is, so I went a different route.