GMC Sierra 3500HD 2001 Owner's Manual page 217

Headlamps
-
Sealed Beam Headlamps
2. Pull the headlamp out and remove the retainer.
6-34
1. Remove the four
screws from the
headlamp retainer.
4. Plug in the new headlamp and put it in place.
5. Install the retainer to the headlamp and tighten
the screws.
3. Unplug and remove
the headlamp.