The Lincoln Mark III uses an H5001 bulb size for high beam headlights and an H5006 bulb size for low beam headlights. The replacement chart covers vehicle production years spanning 1968 to 1971 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 Lincoln Mark III uses two distinct sealed beam types across its 1968-1971 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 recognized in both 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 applicable in the United States and Canada.
Both the H5001 and H5006 are sealed beam assemblies, meaning the lens, reflector, and filament form a single unit. When the filament fails, the entire assembly requires replacement rather than an internal bulb swap.
The square profile of the H5001 and the round profile of the H5006 make the two units physically incompatible with each other's housings, and one cannot substitute for the other.
The H5001 high beam and H5006 low beam fitments remain consistent across all four model years of the Lincoln Mark III, from 1968 through 1971, with no variation in bulb size between those years.