Harley-Davidson FX Super Glide Tail Light Bulb Size

Harley-Davidson FX Super Glide tail light utilizes a 1157 bulb size for replacement applications. The replacement chart covers 1971 to 1978 vehicle production 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	US Type	EU Type	Shop
1971-1978	1157	P21/5W	Check Price

Bulb Specifications

Description	Type	Shop
ANSI standard (US & Canada). Dual-filament bulb with BAY15d bayonet base. 12V, 21W/5W.	1157	Check Price
ECE standard (Europe & worldwide). Dual-filament signalling bulb with BAY15d bayonet base. 12V, 21W/5W.	P21/5W	Check Price

Other Locations

Additional Notes

The 1157 is the tail light bulb type specified for the Harley-Davidson FX Super Glide across all listed model years, spanning 1971-1978.
The 1157 is an ANSI-standardized bulb type recognized across the United States and Canada, meaning it conforms to a defined set of electrical and physical parameters shared by all compliant manufacturers.
As a dual-filament bulb, the 1157 operates two separate tungsten filaments within a single glass envelope, allowing it to serve both a low-intensity running light function at 5W and a high-intensity braking or signaling function at 21W.
The 1157 uses a BAY15d bayonet base, a two-pin offset base type in which the two pins are positioned at different heights along the base. This offset arrangement prevents incorrect single-filament bulbs from being seated in the socket.
The bulb operates on a 12-volt electrical system, consistent with the standard automotive and motorcycle electrical architecture of that era.
Because the BAY15d base is offset, substituting a BAY15s base bulb, which carries only a single filament and symmetrically placed pins, would result in an improper fit and loss of dual-filament functionality.