All other rear lights working perfectly. Had an interesting experience. I live in a very hot summer climate. My XK8 has been kept in my garage when not drivng for the last 20 years but this summer no garage available. The plastic bracket that holds the rear view mirror melted and the melted plastic ran down into my jgate. Unbelievable right? It happened. Is it possible some damage or any interference could have caused both the high mount and the rear fog lights to cease functioning? I've pulled and replaced the relays and fuses for the rear lights but no change. Any other ideas greatly appreciated. If a loose wire is the issue how do I track down the culprit for the high mount?

 

Are you sure your lights were working before the mirror bracket melted - sounds like coincidence or the high temperatures melted something else. You've already checked the relays and fuses, so the next step is to try jumping the relays and see if the lights come on. Another simple check is to make sure you have power and ground where you expect it to be in the trunk fuse box - you need a multimeter, or even better, a test bulb to check that.