Harley-Davidson FLHTCUTG Tri Glide Ultra Turn Signal Bulb Size

Harley-Davidson FLHTCUTG Tri Glide Ultra rear turn signal bulb uses a 3157 size, with P21W designation for this specific bulb. The replacement chart covers 2011 through 2020 vehicle production years and contains bulb size specifications.

The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.

Rear Turn Signal

Years	Bulb Size
2014-2020	3157
2011-2013	P21W

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Dual-filament wedge bulb (T25). 12V, 27W/7W.	3157
ECE standard (Europe & worldwide). Single-filament signalling bulb with BA15s bayonet base. 12V, 21W.	P21W

Other Locations

Additional Notes

The 3157 is an ANSI-standard dual-filament bulb operating at 12V with a 27W bright filament and a 7W dim filament, housed in a T25 wedge form factor. Its dual-filament design allows a single bulb to serve both turn signal and running light functions simultaneously.
The P21W follows the ECE standard used in European and worldwide markets. It is a single-filament bulb rated at 12V and 21W, fitted with a BA15s bayonet base, which is a single-contact base with one locating pin on the side of the cap.
The Harley-Davidson FLHTCUTG Tri Glide Ultra rear turn signal uses the 3157 bulb for model years 2014-2020, representing the majority of the listed fitment range.
Model years 2011-2013 of the same vehicle use the P21W instead of the 3157. These two bulb types are not interchangeable due to differences in base design, filament count, and governing standards.
The transition between P21W and 3157 fitment occurred between the 2013 and 2014 model years, reflecting a shift from ECE-standard to ANSI-standard rear turn signal hardware.
Because the 3157 uses a wedge base and the P21W uses a BA15s bayonet base, the socket configurations in the vehicle differ between the two fitment groups, making cross-year substitution physically incompatible without modification.