Amazon.com: Metra 40-GM10 GM Antenna Adapter: Car Electronics
Amazon.com: Metra 70-2003 Radio Wiring Harness For GM 98-Up Harness: Car Electronics

i used these two in my base 05 grand prix and have never had any problems... i did lose my chimes however (i find this to be a good thing because i hate the annoying things) and i think i lost my onstar... however i never have even attempted to use it so i couldnt tell you if i did or didnt actually lose it