Harley-Davidson FXS Low Rider Tail Light Bulb Size

Harley-Davidson FXS Low Rider tail light uses a 1157 bulb size for the rear lighting assembly. The replacement chart covers 1977 to 1982 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.

Bulb Size by Year Range

Years	Bulb Size
1977-1982	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 sole tail light bulb size listed across all specification rows for the Harley-Davidson FXS Low Rider, covering the 1977-1982 model years.
The 1157 is an ANSI-standardized bulb type recognized in both the United States and Canada, meaning it conforms to a defined set of electrical and physical parameters shared across manufacturers.
The bulb operates on a dual-filament design, which allows a single unit to serve two distinct lighting functions, typically a lower-intensity running light and a higher-intensity brake light signal.
The 1157 uses a BAY15d bayonet base, a two-pin offset base type where the two pins are positioned at different heights to prevent incorrect insertion orientation during fitment.
The bulb is rated at 12 volts, consistent with the standard electrical system voltage found in most production motorcycles of that era.
The dual wattage rating of 21W and 5W corresponds to the two filaments: the 21W filament serves the higher-draw function and the 5W filament serves the lower-draw function.
Because the BAY15d base uses offset pins, substitution with single-filament bayonet bulbs or those with a symmetrical two-pin base would result in an incompatible fitment.