The White/GMC WCL headlight bulb size specifications indicate 9004 and H6024 bulb options for both high beam and low beam applications. The replacement chart covers 1988 through 1993 vehicle production years with corresponding bulb size data.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The White/GMC WCL used two distinct headlamp systems across the 1988-1993 model years: composite headlamps and sealed beam headlamps. Each system requires a different bulb type, making headlamp configuration a critical factor before sourcing a replacement.
The 9004 is a dual-filament halogen bulb operating at 12V with a wattage rating of 65W on the high beam filament and 45W on the low beam filament. Its P29t base is a proprietary connector type, meaning it is not interchangeable with single-filament halogen bulbs or other base configurations.
Because the 9004 contains both high and low beam filaments within a single housing, it serves both the high beam and low beam functions on WCL models equipped with composite headlamps. A single bulb failure can therefore affect both beam modes simultaneously.
The H6024 is a 7-inch round sealed beam unit operating at 12V. Unlike the 9004, it is not a replaceable bulb in the conventional sense. The entire sealed beam unit functions as both the lens and the light source, and the whole assembly is replaced as one piece when the unit fails.
The 9004 and H6024 are both ANSI-standardized types recognized in the United States and Canada, meaning both conform to defined performance and dimensional standards within those markets.
The two headlamp types are not interchangeable. Composite headlamp housings are designed to accept the 9004 bulb via its P29t socket, while sealed beam housings are designed to receive the H6024 as a complete unit. Installing the wrong type is not physically compatible with the opposing housing design.