Harley-Davidson FXDF Fat Bob Tail Light Bulb Size

Harley-Davidson FXDF Fat Bob tail light uses a 3157 bulb size for replacement applications. The replacement chart covers 2012 to 2013 vehicle production 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
2012-2013	3157

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Dual-filament wedge bulb (T25). 12V, 27W/7W.	3157

Other Locations

Additional Notes

The 3157 is an ANSI-standardized bulb type used in both the United States and Canada, operating at 12 volts with a dual-filament design rated at 27 watts for the stop/brake function and 7 watts for the tail/running function.
The T25 designation refers to the bulb's wedge-base form factor, which is a common physical format in automotive lighting applications.
The Harley-Davidson FXDF Fat Bob uses the 3157 bulb for the tail light position across the 2012-2013 model years.
The dual-filament construction of the 3157 means a single bulb serves two distinct lighting functions simultaneously, distinguishing it from single-filament alternatives such as the 3156, which shares the same base but is not interchangeable due to its single-filament configuration.