Prevost Marathon Headlight Bulb Size

The Prevost Marathon high beam headlight uses H4656 or H4651 bulb sizes, while the low beam headlight requires an H4656 bulb size. The replacement chart covers vehicle production years spanning 1984 to 1986 with corresponding bulb specifications.

The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.

High Beam Headlight

Years	Bulb Type	Shop
1984-1986	H4651	Check Price
1984-1986	H4656	Check Price

Low Beam Headlight

Years	Bulb Type	Shop
1984-1986	H4656	Check Price

Bulb Specifications

Description	Type	Shop
ANSI standard (US & Canada). 4x6-inch rectangular sealed beam unit. Not a replaceable bulb — the entire unit is replaced. 12V.	H4651	Check Price
ANSI standard (US & Canada). 4x6-inch rectangular sealed beam unit. Not a replaceable bulb — the entire unit is replaced. 12V.	H4656	Check Price

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Additional Notes

The Prevost Marathon uses two bulb types across its headlight system for the 1984-1986 model years: H4656 and H4651, both of which are ANSI-standardized sealed beam units recognized in the United States and Canada.
Both the H4656 and H4651 are 4x6-inch rectangular sealed beam units operating at 12 volts. In a sealed beam design, the reflector, lens, and filament are fused into a single glass envelope, meaning the entire unit is replaced rather than an internal bulb.
The H4656 appears across all three listed model years in both the high beam and low beam positions, making it the more broadly applied of the two sealed beam types in this specification set.
The H4651 is listed exclusively for the high beam position across the 1984-1986 model years and does not appear in the low beam specifications.
Because the H4656 and H4651 share the same 4x6-inch rectangular form factor and voltage rating, they may appear physically similar, but they are listed as distinct part numbers and serve different beam positions, which carries implications for correct fitment.
The low beam headlight position on the Prevost Marathon is served solely by the H4656 for all three listed model years, with no alternative bulb size specified for that position.