Remove the front grill to access the headlights.
If its anything like my 04 sonoma, there should be two flat pins which hold the headlight assembly in place. the pins come out, the socket for the bulbs become acessible. twist out and replace. .
More that likely the headlight switch is bad. Turn your headlights on and when they start to flicker tap on the headlight switch real fast. If they flicker to you tapping on the switch, that's the problem. They had problems with that switch around that year. It's a pretty cheap fix and you can do it your self quickly. Can also be a sign of a failing alternator.
you have to remove the headlight bezel. there is 4 screws around the headlight and possibly 2 along the side of the signal light
2002 GMC Sonoma headlight bulb replacement: Purchase the correct replacement headlight bulb(s) first, before disassembling the vehicle. See sources and related links below for replacement bulb information. Then consult your owner's manual for the headlight bulb replacement procedure. As simple as it sounds, the owner's manual is the best place to start for bulb replacement instructions and illustrations. You may want to consider replacing both left and right at the same time in order to keep brightness and color equal (optional).
The complete headlight bucket assembly comes out so you can replace the bulbs easily. Open the hood, stand in front of said headlight, notice two locking tabs sticking up behind the headlight bucket, with a little effort pull up and wiggle each tab out, now wiggle the entire headlight assembly out in the open, twist and remove headlight socket in question, reverse proceedure to install.
Sonoma is a historically significant city in Sonoma Valley, Sonoma County, California, United States, about 50 miles north of San Francisco.
The address of the Sonoma Valley Regional Library is: 755 West Napa Street, Sonoma, 95476 6412
If you look righ behind the nlight you will see two black slide clips. pull them up and roll light out from top to bottom,
The address of the Sonoma League For Historic Preservation is: Po Box 766, Sonoma, CA 95476-0766
The address of the Sonoma Valley Museum Of Art is: Po Box 322, Sonoma, CA 95476-0322
The address of the Sonoma Valley Historical Society is: Po Box 861, Sonoma, CA 95476-0861