I have a 989 XJS convertible. When I open the door both interior lights come on as they should. When I close the door they go off as they should. When i press the interior light button on the dash only the passenger light turns on. Any ideas what the problem could be. I know nothing about electrical wiring.

 

Completely NORMAL.

I had this argument with a customer a few decades ago.(DO NOT ANNOY the driver when the interior light is enabled)

 

Seems a little weird but i will take your word in it. Thanks

 

No weird. It is so the passenger can switch on the light, for instance to read a map (an art that needs explaining to those under 35!) without affecting the night vision of the driver.
Having said which, the lights are so dim I do not think they could affect the driver's vision!

 

The lady (customer) that complained about the way the interior lights worked actually wanted me to RE-WIRE them to work TOGETHER when the switch was used.(I declined)