GMC C15 headlight bulbs utilize H6024 and H5001 sizes for high beam applications, with H6024 and H5006 sizes for low beam configurations in this particular bulb size chart. The replacement chart covers vehicle production spanning 1967 to 1978, documenting headlight bulb specifications across the model's manufacturing period.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The GMC C15 uses two distinct sealed beam types across its 1967-1978 model range: the H6024 and the H5001/H5006 pairing, with the transition occurring between the 1972 and 1973 model years.
The H6024 is a 7-inch round sealed beam unit operating at 12V and conforming to ANSI standards applicable in both the United States and Canada. It serves as both the high beam and low beam unit for the 1973-1978 model years, meaning a single bulb type covers both functions in those years.
For the 1967-1972 model years, the GMC C15 uses a split-type sealed beam arrangement, where the high beam and low beam are handled by two different units: the H5001 and the H5006, respectively.
The H5001 is a 4-inch square sealed beam unit rated at 12V and built to ANSI standards. Its square form factor distinguishes it physically from the round units used elsewhere in this specification set.
The H5006 is a 5.75-inch round sealed beam unit, also rated at 12V and conforming to ANSI standards. Though round like the H6024, it is a smaller unit and the two are not interchangeable.
All three bulb types in these specifications are sealed beam units, meaning the lens, reflector, and filament are fused into a single assembly. Replacement requires substituting the entire unit rather than an internal bulb component.
The H5001 and H5006 are not interchangeable with each other despite both being used on the same vehicle in the same years, as they serve different beam functions and differ in physical size and form factor.
The shift from the H5001/H5006 pairing to the H6024 for both beam functions represents a change in headlight configuration, with the later 1973-1978 years using a single standardized round unit across both high and low beam positions.