Installation Procedure

Install the bulb to the socket.
Rotate the bulb 1/4 turn to lock into place.

Fig 1: Removing/Installing License Lamp Bulb
Courtesy of GENERAL MOTORS CORP.
Install the lamp's retainer to the rear bumper by pushing the lamp up and in, then tilting the bottom of the lamp into the bumper.
Install the lamp to the rear bumper by rotating it clockwise or counter-clockwise.

Fig 2: Removing/Installing License Lamp (w/ Step Bumper)
Courtesy of GENERAL MOTORS CORP.