The Autocar AT high beam headlight uses an H4651 bulb size, while low beam headlights use H4656 or H4652 bulb sizes. The replacement chart covers 1983 through 1988 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 H4651, H4656, and H4652 are all ANSI-standardized sealed beam units used across the 1983-1988 Autocar AT, each operating at 12V and sharing a 4x6-inch rectangular form factor. Because the light source is fused within the lens and reflector assembly, the entire unit is replaced rather than an internal bulb.
The H4651 serves as the high beam unit across all six model years covered in the specifications, from 1983 through 1988, with no variation in that position over the entire period.
The H4652 is described as a variant of the H4651. Despite sharing the same rectangular sealed beam construction and 12V rating, the two are distinct ANSI designations and are not listed interchangeably within the specifications.
The low beam position on the Autocar AT does not use a single consistent unit across all years. The H4656 is fitted for 1985-1986 and 1988, while the H4652 appears in 1983-1984 and 1987, indicating that the low beam specification alternates between the two units depending on the model year.
Because the H4651 and H4652 are related but distinct ANSI designations, substituting one for the other in the low beam position would not reflect the fitment data provided in the specifications.
All three sealed beam types conform to ANSI standards recognized in both the United States and Canada, meaning the physical and electrical specifications are governed by a shared regulatory framework across both markets.