Triumph Bonneville SE Tail Light Bulb Size

The Triumph Bonneville SE tail light requires a P21/5W bulb size for proper illumination. Replacement bulb specifications in the chart cover 2009 through 2013 vehicle production years.

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
2009-2013	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 Triumph Bonneville SE uses the P21/5W bulb for its tail light across the 2009-2013 model years.
The P21/5W is a dual-filament bulb, meaning it contains two separate filaments within a single glass envelope, one rated at 21 watts and the other at 5 watts.
In tail light applications, the higher 21W filament typically serves the brake light function, while the lower 5W filament handles the running light function.
The P21/5W uses a BAY15d bayonet base, which features two offset pins at different heights to ensure the bulb is inserted in the correct rotational position, preventing filament misalignment.
The BAY15d base is not interchangeable with the BA15d base, which has pins at the same height, making correct base identification important when sourcing a replacement.
The P21/5W operates on a 12V electrical system, consistent with standard automotive voltage.
This bulb type is governed by ECE regulations, a standard recognized across Europe and many other markets worldwide.