GMC 2004 Sierra - Manual (Page 469)

Center High-Mounted Stoplamp
(CHMSL) and Cargo Lamp
1. Remove the screws and lift off the lamp assembly.
A. Cargo Lamps
B. Center High-Mounted Stoplamps
2. Remove the CHMSL bulb holder back plate from
the housing by pressing the release tabs.
3. Remove the CHMSL bulb by pulling the bulb
straight out from the holder back plate. Remove
a cargo bulb by turning the socket counterclockwise
and pulling the bulb straight out.
5-69