WARNING: This page is about a different car, the 2003 Cadillac CTS. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Radio/Audio System Schematics (Radio/Amplifier Power And Grounds)
Courtesy of GENERAL MOTORS CORP.
Fig 2: Radio/Audio System Schematics (Amplifier And Speakers W/U57)
Courtesy of GENERAL MOTORS CORP.
Fig 3: Radio/Audio System Schematics (Amplifier And Speakers W/U66)
Courtesy of GENERAL MOTORS CORP.
Fig 4: Radio/Audio System Schematics (Radio Antenna Module)