GMC 2004 Sierra - Manual (Page 470)

4. If a CHMSL bulb is replaced, put the new bulb into
the socket and press it in until it is tight.
If a cargo lamp is replaced, put a new cargo lamp
bulb into the socket and press it in until it is
tight before turning the socket counterclockwise.
5. Put the bulb holder back plate into the lamp
housing.
6. Reinstall the lamp assembly and tighten the screws.
Pickup Box Identification and
Fender Marker Lamps
1. Remove the screws and lamp assembly.
2. Unplug the lamp assembly harness.
3. Gently pry the individual lamp from the lamp
housing.
4. Unplug the lamp.
5. Plug in a new lamp and snap it into the housing.
6. Reinstall the lamp housing.
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