If there is a fuse that supplies power to the BCM (MALL), pull that fuse and check to see if interior lights extinguish. This is just a quick check to see if in fact the BCM is turning on the int. lighting. It could possibly be a lack of ground problem with any of the controlling devices that input to the BCM to turn the int. lighting off. Door latch switches come to mind. Run the MALL diagnostic as outlined by dillcc, I'm curious to see the results. Just some thoughts.

Here is the link to the whole thread that dillcc posted with some of the fuse checks and such identified. Hopefully, one of the fuse checks will provide a simple fix.

http://www.bonnevilleclub.com/forum/...highlight=mall