GMC SIERRA CK2 1999 Owner's Manual page 329

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.
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3. Remove the screws
from the bulb retainer
and take it off the
lamp assembly.
4. Pull the old bulb straight
out of the socket.
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