Triumph Rocket III Classic Brake Bulb Size

The Triumph Rocket III Classic brake bulb uses a P21/5W size for replacement applications across the specified model line. The replacement chart covers vehicle production years from 2006 through 2009 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
2006-2009	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 brake bulb type used across all listed model years of the Triumph Rocket III Classic, spanning 2006-2009.
The P21/5W is a dual-filament bulb, with one filament rated at 21 watts for braking and turn signal functions, and a second filament rated at 5 watts for running light or tail light functions.
The bulb operates on a 12-volt electrical system, consistent with standard motorcycle electrical architecture.
The P21/5W uses a BAY15d bayonet base, which is an offset twin-pin fitting. The asymmetric pin placement of the BAY15d base prevents incorrect installation orientation, ensuring the higher-wattage filament is correctly aligned with the brake circuit.
The P21/5W conforms to ECE (Economic Commission for Europe) standards, indicating it is designed for use in European and international markets rather than SAE-regulated North American specifications.
Because the BAY15d base is specific to the P21/5W type, substitution with single-filament bulbs or bulbs carrying a different base type, such as the BA15s or BAY15s, is not compatible with this fitment.