I have a 2001 XJ8 Vanden Plas. I first got the check rear light message and the passenger side brake light wouldn't go out. We disconnected the bulb so the battery wouldnt run down for the night.
We replaced the bulb but the light would not come on when I stepped on the brake. We replaced the circuit board but still not working.
We then took it to a European car repair. The mechanic says it is the security module and I need to take it to a Jag dealer for replacement.. Any thoughts on this before I take it to the dealer?

 

It does happen with them, there's chips on the board in the module that can go bad. There have been people who have replaced them, and a couple on here too have been able to. Barring that though, it would need replacement. I had the same issue with mine, I just bypassed it to the yellow wiring plug back there and just deal with the message on the dash when using the brakes.

 

The grounds on the lamp assembly go bad

as well as cheap bulbs don't pass enough current which triggers the lamp out light