The Kenworth C550 high beam headlight uses an H4651 bulb size, while low beam headlights require either H4656 or H4652 bulb sizes. The replacement chart covers vehicle production years from 1986 to 1994 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 operating at 12V, meaning the entire lens-reflector-filament assembly is replaced as one piece rather than housing a separate replaceable bulb inside.
All three bulb types share the same 4x6-inch rectangular sealed beam form factor under the ANSI standard recognized in both the United States and Canada.
The Kenworth C550 uses the H4651 exclusively for the high beam headlight position across all model years from 1986-1994, indicating no variation in that position throughout the listed production span.
The H4652 is specified as a variant of the H4651. Although both share the same sealed beam format and voltage rating, they are distinct part numbers and are not listed as interchangeable within these specifications.
The low beam headlight position on the Kenworth C550 alternates between the H4656 and H4652 depending on the model year, with H4652 fitted to 1986-1987, 1991, and 1993, while H4656 is fitted to 1988-1990, 1992, and 1994.
Because the low beam specification differs between adjacent model years, substituting a sealed beam unit from a nearby year without confirming the exact part number risks installing an incorrect variant in that position.
The shared 4x6-inch rectangular form factor across H4651, H4652, and H4656 is a standardized ANSI housing size, which means physical fitment alone does not confirm electrical or photometric compatibility between these part numbers.