I had this happening when I first got my 00 Grand Prix back in 04... I bought the car from a bank because it was repossessed they had it rewired with the factory alarm shut off and that little seatbelt light has something to do with it being rewired. It never drained my battery but after a couple months of having it I took to Pontiac to a buddy of mine that worked there and they fixed it and I cannot remember what they did!!!! Sry!!! Lol