WARNING: This page is about a different car, the 2007 Cadillac CTS. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Power, Ground, and GMLAN Bus Schematics
Courtesy of GENERAL MOTORS CORP.
Fig 2: Class 2 Serial Data Bus Schematics - LHD - 1 of 2
Courtesy of GENERAL MOTORS CORP.
Fig 3: Class 2 Serial Data Bus Schematics - LHD - 2 of 2
Courtesy of GENERAL MOTORS CORP.
Fig 4: Class 2 Serial Data Bus Schematics - RHD - 1 of 2
Courtesy of GENERAL MOTORS CORP.
Fig 5: Class 2 Serial Data Bus Schematics - RHD - 2 of 2