The Mazda Cosmo high beam headlight uses an H5001 bulb size while the low beam headlight requires an H5006 bulb size. The replacement chart covers vehicle production spanning 1976 to 1978.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Mazda Cosmo uses two distinct sealed beam unit types across its 1976-1978 model years: the H5001 for high beam and the H5006 for low beam.
The H5001 is a 4-inch square sealed beam unit operating at 12V. It conforms to ANSI standards applicable in the United States and Canada.
The H5006 is a 5.75-inch round sealed beam unit, also rated at 12V and built to the same ANSI standard as the H5001.
Neither the H5001 nor the H5006 contains a replaceable bulb element. When either unit fails, the entire sealed assembly requires replacement.
The square profile of the H5001 and the round profile of the H5006 make the two units physically incompatible with each other's housings, precluding any interchangeability between the high beam and low beam positions.
Both units share the same 12V operating voltage, which reflects the standard automotive electrical system voltage of the era.
The H5001 and H5006 designations follow ANSI standardization, meaning units from different manufacturers carrying the same designation are generally interchangeable as direct replacements.