GMC K25 high beam and low beam headlight bulbs utilize H6024 and H5001 sizes for high beam applications, with H6024 and H5006 sizes for low beam configurations. The replacement chart covers 1967 to 1978 model years with corresponding bulb size specifications for each production interval.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The GMC K25 headlight specifications span the 1967-1978 model years, with two distinct sealed beam configurations used across that range depending on the model year.
The H6024 is a 7-inch round sealed beam unit operating at 12V and conforming to ANSI standards applicable in the US and Canada. It serves as both the high beam and low beam headlight on the GMC K25 for the 1973-1978 model years, meaning a single bulb type covers both functions in a dual-beam arrangement.
The H5001 is a 4-inch square sealed beam unit, also rated at 12V and built to the same ANSI standard. It functions as the high beam headlight on the GMC K25 for the 1967-1972 model years.
The H5006 is a 5.75-inch round sealed beam unit at 12V, likewise ANSI-rated. It serves as the low beam headlight on the GMC K25 for the 1967-1972 model years, pairing with the H5001 high beam in a four-lamp headlight system where high and low beams are housed in separate units.
All three bulb types are sealed beam units, meaning the lens, reflector, and filament are fused into a single assembly. When a filament fails, the entire unit requires replacement rather than just an internal bulb.
The 1967-1972 configuration uses two different sealed beam types per side, H5001 for high beam and H5006 for low beam, making correct position placement critical during replacement since the two units are not interchangeable with each other.
The 1973-1978 configuration uses the H6024 for both high and low beam functions, which is physically and functionally distinct from either unit used in the earlier 1967-1972 system and is not a cross-compatible replacement for the H5001 or H5006.
The shift from the H5001 and H5006 pairing to the single H6024 type between the 1972 and 1973 model years represents a change in headlight system architecture, from a four-lamp setup with separate high and low beam units to a two-lamp setup using a dual-filament sealed beam.