WARNING: This page is about a different car, the 2002 Pontiac Aztek and 2002 Buick Rendezvous. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Tailgate Audio Controls Inoperative (1 Of 2)
Courtesy of GENERAL MOTORS CORP.
Fig 2: Tailgate Audio Controls Inoperative (2 Of 2)