WARNING: This page is about a different car, the 2007 Chevrolet Malibu. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: View Of Rear Cargo Light
Courtesy of GENERAL MOTORS CORP.
Connect the electrical connector
Fig 2: View Of Cargo Lamp From Rear Quarter Trim Panel
Courtesy of GENERAL MOTORS CORP.
Install the cargo lamp in the rear quarter trim panel.