2012 GMC Sierra Owner's Manual - Page 426

10-40 Vehicle Care 3. When replacing a bulb on the passenger side, remove the Engine Air Cleaner cover. See Engine Air Cleaner/Filter on page 10‑17 for more information. 4. Reach in and access the bulb sockets from inside the engine compartment. 5. Turn the bulb socket counterclockwise to remove it from the headlamp assembly and pull it straight out. 6. Unplug the electrical connector from the old bulb by releasing the clips on the bulb socket. 7. Replace it with a new bulb. 8. Plug in the electrical connector. 9. Reinstall the new bulb socket into the headlamp assembly and turn it clockwise to secure. Pick-Up Box Identification and Fender Marker Lamps The pick-up box identification lamps are LEDs. For replacement of the LED lighting assembly contact your dealer. To replace a pickup box fender marker lamp bulb: 1. Press the tab from the back to remove the lamp. 2. Turn the bulb socket counterclockwise to remove from the lamp assembly. 3. Gently pry the bulb from the socket. 4. Install the new bulb in socket. 5. Reinstall socket into lamp assembly. 6. Reinstall the lamp assembly. Taillamps (Chassis Cab Models) A. Backup Lamp B. Stoplamp/Taillamp/Turn Signal Lamp To replace one of these bulbs: 1. Remove the four screws. 2. Lift the lens off the lamp assembly. 3. Turn the old bulb counterclockwise and pull the it straight out from the socket.