GMC 2004 Sierra - Manual (Page 465)

If your vehicle has one pin on the headlamp
assembly, remove the pin. To remove the pin, turn
the pin up and pull it out straight out.
A. Low-Beam Headlamp
B. High-Beam Headlamp
2. Pull the headlamp assembly out.
3. Unplug the electrical connector.
4. Turn the old bulb counterclockwise and remove it
from the headlamp assembly.
5. Put the new bulb into the assembly and turn it
clockwise until it is tight. Use care not to touch
the bulb with your fingers or hands.
6. Plug in the electrical connector.
7. Put the headlamp assembly back into the vehicle.
Install and tighten the two pins. If your vehicle has
one pin, install it and turn it into the locking
feature.
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