GMC 2009 Sierra - Manual (Page 368)

4. Press the release tab, if the vehicle has one,
and turn the bulb socket counterclockwise to
remove it from the taillamp housing.
5. Pull the old bulb straight out from the socket.
6. Press a new bulb into the socket and turn the
socket clockwise into the taillamp housing until
it clicks.
7. Reinstall the taillamp assembly.
License Plate Lamp
To replace one of these bulbs:
1. Reach under the rear bumper for the bulb socket.
2. Turn the bulb socket counterclockwise and pull
the bulb socket out of the connector.
3. Pull the old bulb from the bulb socket, keeping
the bulb straight as you pull it out.
4. Install the new bulb.
5. Reverse Steps 1 through 3 to reinstall the
bulb socket.
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