GMC P15 / P1500 high beam headlight bulbs use H5001 size while low beam headlight bulbs use H6006 size. The replacement chart covers 1967 through 1972 vehicle 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 GMC P15 / P1500 uses the H5001 sealed beam unit for high beam headlights across all listed model years, 1967-1972.
The H5001 is a 4-inch square sealed beam unit operating at 12V, conforming to ANSI standards recognized in both the United States and Canada. The entire unit is replaced rather than an internal filament or bulb.
The low beam headlight position uses the H5006 sealed beam unit across the same 1967-1972 model year range.
The H5006 is a 5.75-inch round sealed beam unit, also rated at 12V and built to the same ANSI standard. Like the H5001, it is a non-serviceable unit requiring full replacement when it fails.
Because the H5001 and H5006 are physically distinct, with one being a 4-inch square form and the other a 5.75-inch round form, the two units are not interchangeable between the high beam and low beam positions.
The sealed beam construction of both units means the lens, reflector, and filament are fused into a single assembly, which was a common design standard for vehicle headlighting of that period under ANSI regulation.