Mercury Zephyr high beam headlight bulbs use H4651 size, while low beam bulbs use H4656 or H4652 size specifications. The replacement chart covers 1978 to 1983 model years with corresponding bulb size data.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Mercury Zephyr uses sealed beam headlight units across all listed model years (1978-1983), meaning the lens, reflector, and filament are fused into a single glass assembly. When the filament fails, the entire unit is replaced rather than an internal bulb.
All three headlight types found in these specifications, the H4651, H4652, and H4656, conform to ANSI standards recognized in both the United States and Canada. Each operates at 12 volts and shares the same 4x6-inch rectangular sealed beam form factor.
The H4651 is the sole bulb size used for the high beam position across all six model years (1978-1983) of the Mercury Zephyr covered in these specifications.
The low beam position alternates between two sealed beam types depending on the model year. The H4656 was fitted in 1979, 1981, and 1983, while the H4652 was fitted in 1978, 1980, and 1982.
The H4652 is described as a variant of the H4651. Despite sharing the same physical form factor, these two types are not listed as interchangeable, and substituting one for the other in the low beam position is not supported by these specifications.
The H4651 and H4656 occupy different positions in the headlight system and serve distinct functions. Using an H4651 high beam unit in a low beam socket, or vice versa, is not indicated as a valid substitution in these specifications.