The White/GMC WHS headlight bulb uses a 9004 or H6024 size for both high beam and low beam applications. The replacement chart covers 1988 to 1991 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 WHS used two distinct headlamp systems across the 1988-1991 model years: a composite headlamp configuration and a sealed beam headlamp configuration. The correct bulb type depends entirely on which system is installed on a given vehicle.
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. It uses a P29t base and meets ANSI standards for use in the United States and Canada.
Because the 9004 carries both high and low beam filaments within a single housing, it serves both the high beam and low beam headlight positions on WHS units equipped with composite headlamps. A single bulb type covers both functions in that configuration.
The H6024 is a 7-inch round sealed beam unit rated at 12V and recognized under ANSI standards in the United States and Canada. Unlike the 9004, it is not a replaceable bulb; the entire sealed unit is substituted when the lamp fails.
The H6024 also appears in both the high beam and low beam positions on WHS units fitted with sealed beam headlamps, mirroring the dual-position role of the 9004 on composite-equipped vehicles.
The two headlamp systems are not interchangeable. A vehicle with composite headlamps requires the 9004, while one with sealed beam headlamps requires the H6024. Substituting one type for the other is not supported by the specifications.