I would highly suggest you utilize the gmos 02 interface. It's basically plug and play with the head unit(no need to search for the 12v accy. RAP wire), and you can keep the chimes. The problem with the accy. to the radio is GM uses a 5v relay for the radio. Car turns on, sends 5v to the relays, and switches on the RAP system. Regardless of what you do, as soon as you remove the stock hu, you lose the date in the dic. Another one of those things GM did, that data is stored in the non volatile memory in the hu. If you do plan on just using a harness the 12v RAP wire is behind the glove box, accessible from the door jam panel, it's an orange wire. Hope this helps.
