The Autocar ACL uses H4651 bulb size for high beam headlight and H4652 or H4656 bulb sizes for low beam headlight applications. Replacement chart data covers 1981 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 Autocar ACL uses H4651 sealed beam units for the high beam headlight across all listed model years from 1981-1988, making it the most consistently specified bulb type in these fitment records.
The H4651, H4652, and H4656 are all ANSI-standardized 4x6-inch rectangular sealed beam units operating at 12V. None of them contain a replaceable internal bulb element; the entire sealed unit is the component that is replaced.
The H4652 is a variant of the H4651 and serves as the low beam unit for the ACL across most of the listed years. Both share the same physical format and voltage rating, though they are distinct part numbers with different beam functions.
The low beam position of the 1983 Autocar ACL is fitted with the H4656 rather than the H4652 used in surrounding years. The H4656 is a separate ANSI-designated sealed beam unit within the same 4x6-inch rectangular format.
Because the H4651, H4652, and H4656 are sealed beam units rather than bulb-and-housing assemblies, substituting one designation for another is not a straightforward swap. Each carries a distinct ANSI designation that corresponds to specific photometric output characteristics, meaning fitment of an incorrect unit can affect beam pattern and light distribution.
All three sealed beam types in these specifications conform to ANSI standards recognized in both the United States and Canada, indicating they were designed for North American regulatory compliance.