SAAB 9000 98 Turbo Tail Light blows fuse

Hi This is my Father in Laws car. I am an Electronic Tech I have been trying to help him but we are both stumped.
Here's his report (his name is Bill)
1998 Saab 9000 hatchback, fuse keeps blowing on right tail light and instrument panel light. We rebuilt the tailight assembly and it worked temporarily until the hatchback closed which caused the fuse to blow again. What should we check next ? Perhaps an unrelated electrical problem : the AC continued to run after turning off the engine ! I thought it was the cooling fan so ignored the sound but it drained my battery ! I currently have the 40 amp fuse removed but would like to understand what happened.

Does it have a CD changer in the trunk? Is so check the power connection to the CD changer. Quite often the connector gets 'whacked' by something in the trunk. Also,
Preform this test:
1) Disconnect battery ground.
2) Turn the light switch to the 'park' position.
3) Now measure the resistance between the positive and negative battery terminals. (be sure and leave the battery disconnected)
What did you get?
Now turn the light switch to off and measure again. Any change?