Triumph Rocket III Classic Tourer Brake Bulb Size

The Triumph Rocket III Classic Tourer brake bulb uses a P21/5W size bulb for replacement applications. 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 brake bulb type specified 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 higher 21W filament serves the brake or stop light function, while the lower 5W filament handles the tail or running light function.
The bulb operates on a 12V electrical system, consistent with standard automotive and motorcycle electrical architecture.
The P21/5W uses a BAY15d bayonet base. The BAY15d designation indicates an offset pin configuration, where the two retaining pins are positioned at different heights on the base. This offset is a deliberate design feature that prevents the bulb from being inserted in the wrong orientation, ensuring the correct filament aligns with each circuit.
The P21/5W conforms to ECE (Economic Commission for Europe) standards, a regulatory framework recognized across Europe and numerous other markets worldwide.
The BAY15d base type is distinct from the similarly named BA15d base. The BA15d has pins at equal heights, making it physically incompatible with a BAY15d socket without forced insertion. Substituting one for the other risks incorrect filament alignment or socket damage.
A single-filament P21W bulb shares the same wattage on its primary filament but lacks the secondary 5W filament entirely. It is not a direct replacement for the P21/5W in a dual-circuit brake and tail light application.