WARNING: This page is about a different car, the 2005 GMC Sierra and 2005 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Power, Ground, and Serial Data Schematic
Courtesy of GENERAL MOTORS CORP.
Fig 2: Interior Lights and Interior Lights Dimming References Schematic
Courtesy of GENERAL MOTORS CORP.
Fig 3: Headlights and Exterior Lights References Schematic
Courtesy of GENERAL MOTORS CORP.
Fig 4: Controlled/Monitored Subsystem References Schematic - 1 of 2
Courtesy of GENERAL MOTORS CORP.
Fig 5: Controlled/Monitored Subsystem References Schematic - 2 of 2