Triumph Rocket III Classic Tourer Tail Light Bulb Size

The Triumph Rocket III Classic Tourer tail light requires a P21/5W bulb size for replacement operations. The replacement chart covers vehicle production spanning 2007 to 2011.

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
2007-2011	P21/5W

Bulb Specifications

Description	Bulb Size
ECE standard (Europe & worldwide). Dual-filament signalling bulb with BAY15d bayonet base. 12V, 21W/5W.	P21/5W

Other Locations

Additional Notes

The P21/5W is the sole tail light bulb type listed for the Triumph Rocket III Classic Tourer across the 2007-2011 model years.
The P21/5W is a dual-filament bulb, meaning it contains two separate filaments within a single glass envelope. The 21W filament serves the braking or turn signal function, while the 5W filament handles the running light function.
The bulb operates on a 12V electrical system, which is standard for motorcycle applications in this class.
The P21/5W 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 installation of a single-filament bulb in place of a dual-filament one.
The P21/5W conforms to ECE (Economic Commission for Europe) standards, giving it broad acceptance across European and worldwide markets.
Because the BAY15d base is physically keyed by its offset pins, a single-filament BAY15s bulb cannot be substituted without risk of incorrect circuit assignment, making base-type verification a relevant fitment consideration.