The Autocar S headlight bulb uses H4651 for high beam and H4652 or H4656 for low beam, with each size corresponding to specific lighting functions. The replacement chart covers 1981 through 1983 production years and details bulb size specifications for those model years.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Autocar S uses sealed beam headlight units across its 1981-1983 model years, meaning the entire lens-reflector-filament assembly is replaced as one unit rather than swapping an individual bulb.
All three headlight types specified for the Autocar S, the H4651, H4652, and H4656, conform to ANSI standards recognized in both the United States and Canada and operate on a 12V electrical system.
Each of these sealed beam units follows the 4x6-inch rectangular form factor, a standardized size that was widely adopted in North American vehicle lighting regulations.
The H4651 sealed beam unit serves as the high beam headlight across all three model years, 1981-1983, making it the most consistently specified unit in these headlight fitment records.
The H4652 is described as a variant of the H4651. Despite sharing the same physical form factor and voltage rating, the two units are not interchangeable, as the H4652 is designated specifically for low beam function while the H4651 serves the high beam position.
The 1981 Autocar S low beam headlight uses the H4656, which differs from the H4652 unit adopted for the same position in 1982-1983, indicating a mid-run specification change for the low beam fitment.
Because all listed units are sealed beams rather than bulb-and-housing assemblies, fitment accuracy depends on matching the correct ANSI-designated unit to each specific beam position and model year rather than selecting by filament type alone.