OK... got strange error light light last week saying "check rear lights, cruise control in-op". Found 3rd brake light not illuminating.
Sensible, since tapping the brake disengages the C/C and Jag has logic program to disable until all brake lights are good.
As you may know, JLR has listed part OBS. Had local dealer parts buddy do nationwide and CDN search, NADA. I can find NO used replacements anywhere online that fit an '03! None of my usual sources for a used one has either.
Any suggestions?

 

The high mount stop lamp isn't monitored for bulb failure, so that in itself won't trigger a 'check rear lamps' message.

Check F8 (5A) in the trunk fusebox for the high mount fail.

For the message, check the connections around the tail lamp assemblies and the bulbs & their sockets. It could also be the brake switch assembly,
or an issue with the sensing circuitry inside the SLM. A process of elimination, I'm afraid.

The lamp can be repaired if you can disengage it from the fasteners on the rear glass, but it's incredibly fragile