WARNING: This page is about a different car, the 2009 GMC Envoy and 2009 Chevrolet TrailBlazer. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Power, Ground, Serial Data, and Digital Radio Receiver
Courtesy of GENERAL MOTORS CORP.
Fig 2: Base Radio - without Rear Seat Audio Controls
Courtesy of GENERAL MOTORS CORP.
Fig 3: Base Radio - with Rear Seat Audio Controls
Courtesy of GENERAL MOTORS CORP.
Fig 4: Audio Amplifier Power, Grounds, and Premium Radio Low Level Audi Outputs without Rear Seat Audio Controls
Courtesy of GENERAL MOTORS CORP.
Fig 5: Audio Amplifier Power, Grounds, and Premium Radio Low Level Audi Outputs with Rear Seat Audio Controls