WARNING: This page is about a different car, the 2005 Cadillac STS. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Radio Power, Ground, DLC and Audio Communications Schematics
Courtesy of GENERAL MOTORS CORP.
Fig 2: Speakers Schematics - w/UX8
Courtesy of GENERAL MOTORS CORP.
Fig 3: Speakers Schematics (w/UY5) 1 of 3
Courtesy of GENERAL MOTORS CORP.
Fig 4: Speakers Schematics (w/UY5) 2 of 3
Courtesy of GENERAL MOTORS CORP.
Fig 5: Speakers Schematics (w/UY5) 3 of 3
Courtesy of GENERAL MOTORS CORP.
Fig 6: Radio Antennas, Audio/Video Adapter Schematics