Kenworth C540 high beam headlight bulbs use H4651 size while low beam headlight bulbs use H4656 or H4652 size. The replacement chart covers 1985 to 1993 vehicle 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 and H4656 are ANSI-standardized sealed beam units used across North America, both conforming to the 4x6-inch rectangular form factor and operating at 12V. Because they are sealed beam units, the entire assembly is replaced rather than an internal filament or capsule.
The H4651 serves as the high beam unit in the Kenworth C540 for 1985, 1992, and 1993, while the H4656 fills the low beam role for 1992 and 1993. Both share the same physical sealed beam format, though they are not interchangeable due to differing beam pattern designations within the ANSI standard.
The 1985 Kenworth C540 uses the H4652 for the low beam position rather than the H4656 found in later years. The H4652 is a variant of the H4651 within the same 4x6-inch rectangular sealed beam family, also rated at 12V and governed by the same ANSI standard.
Within the ANSI sealed beam system, different part numbers within the same physical size class denote distinct optical configurations. The H4651, H4652, and H4656 are all 4x6-inch units, but each carries a specific beam pattern, which is why substitution between them is not supported by the specifications.