GMC first used the "Sierra" nameplate in 1975 in trim levels: in order from lowest to highest, these trim levels were: Sierra, Sierra Grande, High Sierra and Sierra Classic. In 1999, however, GMC released a new line of trucks to replace the C- and K-Series pickups and gave it a familiar name: Sierra. In 2007, the Sierra underwent a complete overhaul that included an all-new front fascia and headlights. Replacing the headlight bulbs in the 2008 Sierra requires light mechanical work, but most owners can perform the task.
Proceed to Step 2 if you are replacing the driver-side headlight bulb.
To replace the passenger-side bulb, loosen the four screws securing the top of the air filter housing to the lower half, using a Phillips screwdriver. Lift the cover upward to gain access to the rear of the passenger-side headlight assembly.
Reach behind the headlight assembly and rotate the headlight bulb counterclockwise to unlock it. Pull the headlight bulb and its wiring harness from the headlight assembly. Lift upward on the locking clips on the headlight bulb wiring harness to unlock it and unplug the headlight bulb from the harness.
Hold the new headlight bulb -- No. H11 for the low beam or No. 9005 for the high beam -- by its plastic base to avoid contacting the glass part of the bulb with your bare hands. Plug the wiring harness into the new headlight bulb, then insert the headlight bulb into the headlight assembly and turn it clockwise to lock it in place.
Install the top half of the air filter housing onto the lower half, if applicable, and tighten its screws until they are snug. Close the hood.
