inside lamp does not go out when door is shut and does not

This problem caused my radio to remain on upon vacating the vehicle and eventually killed my battery. The initial incident caused awareness and and I had to turn the radio off manually each time I exit, which is a pain. I took it to a GM technician and was informed that it would cost a significant amount of man hours with no guarantee of success to look into. If I don't want to buy another car, I have to put up with it.