The Triumph Bonneville T120 headlight bulb uses a 9003 size for both high and low beam functions. The replacement chart covers vehicle production years spanning 2016 to 2023 with corresponding bulb size specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Triumph Bonneville T120 uses the 9003 bulb size for both high beam and low beam headlight positions across the 2016-2018 and 2022-2023 model years.
The 9003 is a dual-filament halogen bulb, meaning a single bulb contains two separate filaments to serve both high and low beam functions within one housing.
The 9003 operates on a 12-volt electrical system and draws 60 watts on the high beam filament and 55 watts on the low beam filament.
The 9003 uses a P43t base, which is a bayonet-style mount with a 43mm flange. This base type determines physical fitment into the headlight housing and is not interchangeable with other base configurations.
The 9003 is an ANSI-standardized bulb type recognized in the United States and Canada. It is functionally equivalent to the H4 bulb used under international ECE standards, though the two designations reflect different regulatory frameworks and may carry minor specification differences.
Because the same 9003 bulb serves both beam functions on the Bonneville T120, replacing the headlight bulb addresses both high and low beam output in a single service operation.