The White/GMC WCM headlight bulb size specifications indicate 9004 and H6024 bulb sizes for both high beam and low beam applications. The replacement chart covers vehicle production years spanning 1988 to 1994.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The White/GMC WCM uses two distinct headlamp systems across the 1988-1994 model years: composite headlamps and sealed beam headlamps. The correct bulb type is determined entirely by which headlamp system is installed on the vehicle.
The 9004 is a dual-filament halogen bulb operating on a P29t base at 12V, with filament ratings of 65W for high beam and 45W for low beam. A single 9004 bulb serves both the high beam and low beam functions within a composite headlamp assembly.
The H6024 is a 7-inch round sealed beam unit conforming to ANSI standards for the US and Canadian markets. Unlike the 9004, it is not a replaceable bulb; the entire sealed beam unit is replaced as one piece when the light source fails.
Both the 9004 and H6024 are listed identically for both the high beam and low beam positions across all covered years, reflecting that each headlamp type handles both beam functions within its respective assembly design.
The 9004 and H6024 are not interchangeable. The composite and sealed beam headlamp systems use fundamentally different mounting and optical designs, and the bulb type must match the headlamp assembly present on the vehicle.
Both bulb types carry ANSI certification for the US and Canadian markets, meaning they conform to standardized performance and safety specifications recognized across North America.