GMC C25 headlight bulbs utilize H6024 and H5001 sizes for high beam applications, along with H6024 and H5006 sizes for low beam functions, with each bulb size corresponding to specific lighting requirements. The replacement chart covers 1967 through 1978 model years and details bulb size specifications across the vehicle production range.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The GMC C25 headlight specifications cover the 1967-1978 model years, with two distinct sealed beam configurations appearing across that span depending on the year.
The H6024 is a 7-inch round sealed beam unit operating at 12V and conforming to ANSI standards for the US and Canada. It serves as both the high beam and low beam headlight on the GMC C25 for the 1973-1978 model years, meaning a single bulb type covers both functions in a dual-beam arrangement within one unit.
The H5001 is a 4-inch square sealed beam unit, also rated at 12V and ANSI-standardized. It functions as the high beam headlight on the C25 for the 1967-1972 model years.
The H5006 is a 5.75-inch round sealed beam unit rated at 12V under the same ANSI standard. It serves as the low beam headlight for the 1967-1972 model years, pairing with the H5001 high beam in a four-lamp headlight system where separate units handle each beam function.
All three bulb types, H6024, H5001, and H5006, are sealed beam units. In each case, the entire lens, reflector, and filament assembly is replaced as one piece rather than replacing an internal bulb element.
The shift from the H5001 and H5006 pairing to the single H6024 type occurred between the 1972 and 1973 model years on the C25, reflecting a change in headlight housing configuration.
The H5001 and H5006 are not interchangeable with each other despite both being sealed beam units from the same era. They differ in physical size and beam function, with the square H5001 designated for high beam use and the round H5006 for low beam use.
The H6024 is physically larger than both the H5001 and H5006, and its round 7-inch format is not cross-compatible with either of the earlier sealed beam types used on the 1967-1972 C25.