Although you can hardwire a stereo into this car, it's not recommended. Your car needs a class II data interface for everything to work properly. Metra makes one for your car. the model # XXXXX XXXXX (does not work with onstar). You can pick up one of these or a like model at most any install shop.
Here's a description of this part:
The wiring harness has a white 10-pin female connector (4 pins present) on one end and a gray 24-pin male connector (14 pins present) on the other end. The 10-pin connector plugs into the VT-GMRC-01 and the 24-pin connector interfaces with the existing factory plug.Note: Will not work with OnStar equipped vehiclesCOMPATIBLE VEHICLES:ChevroletAvalanche 2003+ - upCavalier 2000-2003Express 2003Impala 2003 Malibu 2002-2003Tahoe 2003Trailblazer 2002-2003Silverado 2003Suburban 2003 GMCEnvoy 2002-2003Savanna 2003Sierra 2003 Yukon 2003 PontiacAztec 2001-2003Grand Am 2001-2003 GrandPrix 2004Sunfire 2000-2003 OldsmobileAlero 2002-2003Bravada 2002-2003
This will work if you haven't cut off the factory harness. I highly recommend you use this part. If you decide not to, & still want the wire colors, let me know & I can provide that.