Pontiac Grandville headlight bulbs utilize H4651 and H5001 sizes for high beam applications and H4656 and H5006 sizes for low beam functions. The replacement chart covers 1971 through 1975 model 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 Pontiac Grandville uses four distinct sealed beam unit types across its headlight positions and model years: H4651, H5001, H4656, and H5006.
All four sealed beam types in these specifications conform to ANSI standards recognized in both the United States and Canada, and all operate at 12 volts.
Sealed beam units are self-contained assemblies in which the filament, reflector, and lens are fused into a single glass envelope, meaning the entire unit is replaced rather than an internal bulb.
The 1975 Grandville high beam position uses the H4651, a 4x6-inch rectangular sealed beam unit, while the 1971-1974 high beam position uses the H5001, a 4-inch square sealed beam unit.
The H4651 and H4656 share the same 4x6-inch rectangular form factor but serve different beam functions, making them non-interchangeable despite their physical similarity.
The 1975 Grandville low beam position uses the H4656, a 4x6-inch rectangular sealed beam unit, while the 1971-1974 low beam position uses the H5006, a 5.75-inch round sealed beam unit.
The shift from round and square sealed beam units in 1971-1974 to rectangular units in 1975 means that high beam and low beam housings from different model years are not interchangeable.
The H5001 square high beam unit and the H5006 round low beam unit used in 1971-1974 differ in both shape and size, and substituting one for the other is not supported by these specifications.