GMC 2000 Sierra - Manual (Page 345)

yellow blue
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4. If a CHMSL bulb is replaced, put the bulb into the
socket and press it in until it is tight.
5. 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.
6. Put the bulb holder back plate into the lamp housing.
7. Replace the lamp assembly and tighten the screws.
Taillamps (Pickup Models)
1. Open the tailgate.
2. Remove the two rear
lamp assembly screws
near the tailgate latch
and pull out the
lamp assembly.