When I open it up at night sometimes the courtesy lights come on, sometimes not. Occasionally they will turn themselves on after it's open for a bit.

I thought there might be some logic to the conditions that allow them to come on but I can't figure it out.

Any ideas?

 

Try cleaning the latch microswitch with some spray electronic cleaner.

 

Broken wire in the harness - it flexes the trunk is opened/closed.

 

You're talking about an XJ8, he isn't.

 

I stand corrected. You are quite right!