The Buick Somerset high beam headlight uses an H4651 bulb size while the low beam headlight requires an H4656 bulb size. The replacement chart covers 1986 to 1987 model years with corresponding bulb 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 the two bulb types specified for the Buick Somerset across the 1986-1987 model years, serving the high beam and low beam headlight positions respectively.
Both the H4651 and H4656 conform to ANSI standards recognized in the United States and Canada, placing them within a standardized sizing and performance framework common to North American automotive lighting of that era.
Each unit is a 4x6-inch rectangular sealed beam, meaning the lens, reflector, and filament are fused into a single assembly. When the filament fails, the entire sealed unit requires replacement rather than an internal bulb swap.
Both types operate at 12 volts, consistent with the standard electrical system voltage found in passenger vehicles.
The H4651 and H4656 share the same physical format, a 4x6-inch rectangular sealed beam, yet they are not interchangeable. The two types are specified for distinct functions, with the H4651 designated for high beam use and the H4656 for low beam use on the Buick Somerset.