Harley-Davidson FXEF Fat Bob Brake Bulb Size

Harley-Davidson FXEF Fat Bob uses a 1157 bulb size for brake applications. The replacement chart covers 1979 to 1981 model 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.

Bulb Size by Year Range

Years	Bulb Size
1979-1981	1157

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Dual-filament bulb with BAY15d bayonet base. 12V, 21W/5W.	1157

Other Locations

Additional Notes

The 1157 is the brake bulb size specified for the Harley-Davidson FXEF Fat Bob across the 1979-1981 model years.
The 1157 is a dual-filament bulb, meaning it serves two lighting functions within a single unit. In automotive applications, the higher-wattage filament typically handles braking or turn signals, while the lower-wattage filament handles running or parking light duties.
The 1157 operates at 12 volts with a wattage rating of 21W/5W, corresponding to its two filaments respectively.
The 1157 uses a BAY15d bayonet base. The BAY15d designation indicates an offset double-contact base, where the two pins are positioned at different heights to prevent incorrect insertion of a single-filament bulb into a dual-filament socket.
The 1157 is classified under the ANSI standard and is recognized in both the United States and Canada, indicating a standardized specification shared across North American markets.
Because the BAY15d base is offset by design, a single-filament bulb with a BAY15s base is not interchangeable with the 1157, even if the physical housing appears similar. Installing an incompatible base type would prevent proper seating in the socket.