The White/GMC J8C0 headlight bulb utilizes a 9004 or H6024 size for both high beam and low beam functions. The replacement chart covers 1988 to 1989 production years with corresponding bulb size specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The White/GMC J8C0 for model years 1988-1989 accommodates two distinct headlamp system types: composite headlamps and sealed beam headlamps. Each system requires a different bulb or unit, and the two are not interchangeable.
The 9004 is a dual-filament halogen bulb operating at 12V with a high beam output of 65W and a low beam output of 45W. Its P29t base is a single connector that serves both filaments, which allows one bulb to handle both high and low beam functions within a composite headlamp housing.
Because the 9004 handles both high and low beam functions through its dual filaments, the J8C0 with composite headlamps uses the same 9004 bulb size for both the high beam and low beam positions.
The H6024 is a 7-inch round sealed beam unit conforming to ANSI standards applicable in the United States and Canada. Unlike the 9004, it is not a replaceable bulb; the entire sealed unit is replaced when the light source fails.
The H6024 sealed beam unit also serves both the high beam and low beam positions on the J8C0 equipped with sealed beam headlamps, mirroring the dual-position role of the 9004 on composite-equipped vehicles.
Both the 9004 and H6024 conform to ANSI standards for the United States and Canada, indicating that neither is a proprietary or region-specific part outside that market scope.