Dodge Diplomat high beam headlight bulbs use H4651 size while low beam headlight bulbs use H4652 or H4656 size. The replacement chart covers vehicle production spanning 1977 to 1989 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 Dodge Diplomat uses H4651, H4652, and H4656 bulb types across its headlight system. All three are ANSI-standardized sealed beam units recognized in both the United States and Canada, operating at 12 volts.
Each of these bulb types follows the 4x6-inch rectangular sealed beam format. This format was a regulated standard in North America, meaning the physical housing conforms to fixed dimensions shared across compliant units.
Sealed beam units of this type do not contain a replaceable filament or capsule. When a unit fails, the entire assembly is replaced rather than an internal component.
The H4651 serves as the high beam headlight across the full 1977-1989 model range of the Dodge Diplomat without variation.
The H4652 is described as a variant of the H4651. Both share the same 4x6-inch rectangular sealed beam construction and 12-volt rating, though they are designated for different beam functions and are not listed as interchangeable in these specifications.
The low beam headlight position shows fitment variation across model years. The Dodge Diplomat uses the H4656 for the low beam in 1977, 1982, and 1983, while the H4652 fills that position in all other listed years.