WARNING: This page is about a different car, the 2007 Cadillac SRX. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Radio and Amplifier Power, Ground, and Communication Schematic (UQA)
Courtesy of GENERAL MOTORS CORP.
Fig 2: Radio and Amplifier Power, Ground, and Communication Schematic (UQS w/o U42)
Courtesy of GENERAL MOTORS CORP.
Fig 3: Radio, Amplifier, Power, Ground, and Communication Schematic (UQS w/U42)