The White/GMC WHM headlight bulb uses 9004 and H6024 sizes for both high and low beam functions. The replacement chart covers 1988 to 1991 production years with corresponding bulb specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The White/GMC WHM carries two distinct headlamp system types across the 1988, 1989, and 1991 model years: composite headlamps using the 9004 bulb and sealed beam headlamps using the H6024 unit. Both systems serve the high beam and low beam functions within their respective configurations.
The 9004 is a dual-filament halogen bulb rated at 12V with a wattage split of 65W for high beam and 45W for low beam. Its single P29t base housing contains both filaments, which is what allows one bulb to serve both beam functions simultaneously.
The H6024 is a 7-inch round sealed beam unit rated at 12V. Unlike a conventional replaceable bulb, the H6024 integrates the filament, reflector, and lens into one sealed assembly, meaning the entire unit is replaced rather than an internal component.
Both the 9004 and H6024 are ANSI-standardized types recognized in the United States and Canada, meaning their physical and electrical specifications conform to a defined industry standard rather than being proprietary to a single manufacturer.
The 9004 and H6024 are not interchangeable. The 9004 is designed for composite headlamp housings that accept a removable bulb with a P29t base, while the H6024 is a self-contained sealed beam unit requiring a housing designed to hold the entire assembly.
On the White/GMC WHM, the headlamp system type present on a given vehicle determines which replacement part applies. Installing a 9004 bulb is only applicable to units equipped with composite headlamps, and the H6024 applies exclusively to vehicles with sealed beam headlamps.