Made by Metra it's part number GMOS-01. The salesman may try to sell you the GMOS-04 because you have the Monsoon system, but that leads to low audio output using the low-level RCA inputs on the module. Just use the GMOS-01 with it's high-level inputs. Works fine in the Grand Prix. It's going to retain your door chimes, keep your retained accessory feature when the car is off, OnStar (if equipped) and also give you the ignition wire you need for an aftermarket headunit (that the factory harness doesn't have). If you care about your steering wheel controls, you'll need Metra part number ASWC. It plugs right into the GMOS-01 and auto-programs, making life pretty damn easy (read the manual, because certain cars require you holding a button to trigger auto-programming). Retail, you're looking at about 200 bucks for both pieces. But you can probably get them for half that online.