- 1). Turn off your 1991 GMC and wait 30 minutes to begin the replacement procedure if your headlight had been on for a while. Otherwise, prop open the hood.
- 2). Look behind the headlight assembly for the wiring harness. Unplug this cable by pressing in the two side tabs that secure it to the plug and pull it out.
- 3). Twist off the weather cap by turning it counterclockwise.
- 4). Pull the socket out of the assembly by twisting it counterclockwise one-quarter of a turn, or until you see the side tabs appear.
- 5). Pull the bulb out of the socket and insert the new bulb. Be careful not to touch the glass of the bulb with your skin, s this can reduce the life of the bulb. Insert the socket back in the assembly, replace the weather cap and plug in the wiring harness.
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