The White/GMC WCA headlight bulb uses 9004 and H6024 sizes for both high and low beam functions. The replacement chart covers 1988 through 1995 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 WCA used two distinct headlamp systems across the 1988-1995 model years: composite headlamps and sealed beam headlamps. Each system requires a different bulb type, and the two are not interchangeable.
The 9004 is a dual-filament halogen bulb operating at 12V with a wattage rating of 65W on high beam and 45W on low beam. It uses a P29t base and conforms to ANSI standards applicable in both the United States and Canada.
Because the 9004 contains two filaments within a single housing, it serves both the high beam and low beam functions in composite headlamp-equipped WCA models. Only one bulb per headlamp assembly is required for both lighting modes.
The H6024 is a 7-inch round sealed beam unit that operates at 12V and also meets ANSI standards for the US and Canadian markets. Unlike the 9004, the H6024 is not a replaceable bulb; the entire sealed unit is replaced when the lamp fails.
In sealed beam headlamp-equipped WCA models, the H6024 handles both high beam and low beam functions, mirroring the dual-purpose role of the 9004 in composite-equipped vehicles.
The headlamp system type, whether composite or sealed beam, determines which bulb size applies. Fitting a 9004 bulb to a sealed beam housing or an H6024 unit to a composite assembly is not supported by these specifications.
Both the 9004 and H6024 specifications remained unchanged across the entire 1988-1995 production span of the WCA, indicating no bulb specification revision occurred during that period.