WARNING: This page is about a different car, the 2010 Cadillac SRX. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Headrest Displays Power & Ground Circuit Schematic
Courtesy of GENERAL MOTORS CORP.
Fig 2: Driver Headrest Display Signals without ULD, With UYZ Circuit Schematic
Courtesy of GENERAL MOTORS CORP.
Fig 3: Driver Headrest Display Signals Without ULD or UYZ Circuit Schematic