Pontiac Repair: tail lights coming on while car is shut off, pontiac trans port, lamp timer

Question
I have a 1993 Pontiac Trans Port and recently the tail lights started coming on by themselves and usually at night.  If we don't catch it, the battery goes dead.  We disconnected the auto starter, so it isn't that.  The previous owners had a car alarm which they had disconnected.
We have only caught it twice before the battery went dead.  The first time, I just touched the driver's side door and they went out.  The second time, my husband opened the door and they went out.  This last time, I drove it for about 4 weeks before it happened again.  Naturally, we didn't see them so the battery went dead.   
We are very confused. No one we have talked to has any suggestions, except to unhook the auto starter, which we did.  Any suggestions you have will be greatly appreciated.

Answer
Hi Roseanne:

Which light are on at the rear? the parking light, brake lights? How about the license plate lamp as well that is part of the parking lamps. Only the rear lamps? No front ones? How about the dash back lighting like for the radio and the insterment panel? It makes a difference as to how to approach this issue. Being that it's that inintermittant is going to amke it all the hard to find the problem.. If there is any aftermarket stuff still hooked up on this car dis connect it all.. If all of it is off I would Tend to think It's an issue with possably the head lamp swithc assembly on the dash. That had a interior lamp timer and on some cars what was called twilight sentinal which was a lamp timer. whe you shut the car off and the head lamps where on before you turned the car "van" off the head lamps/parking lamps would stay on for a period of time and automatically turn off. It may be in  that timer which is part of the lamp swithc. or you may have a switch in the door that is bad and it is waking up that module and turning the lamps on.. You need to see exactly which lights are on and go from there. Good luck :)