Suzuki Motorcycle S40 Boulevard Turn Signal Bulb Size
Suzuki Motorcycle S40 Boulevard front turn signal bulb size is P21/5W and rear turn signal bulb size is P21W. The replacement chart covers 2005 through 2019 vehicle production years with corresponding bulb specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Suzuki Motorcycle S40 Boulevard uses two distinct bulb types across its turn signal positions: the P21/5W at the front and the P21W at the rear, both conforming to ECE standards recognized in Europe and worldwide. This split fitment applies consistently across the 2005-2019 model years covered in the specifications, with the exception of 2010, for which no data is listed.
The P21/5W is a dual-filament bulb, meaning it contains two separate filaments within a single envelope. It operates on a 12V circuit and draws 21 watts on its primary filament and 5 watts on its secondary filament. It uses a BAY15d bayonet base, which features two offset pins to ensure correct orientation during installation.
The P21W is a single-filament bulb rated at 21 watts on a 12V circuit. It uses a BA15s bayonet base, which has a single pin and allows rotation in either direction. Because the BA15s base lacks the offset-pin alignment of the BAY15d, the two bulb types are not interchangeable despite sharing the same 21-watt primary output.
The base type difference between the front and rear bulbs is a critical fitment consideration for the S40 Boulevard. The front P21/5W requires a BAY15d socket, while the rear P21W requires a BA15s socket. Attempting to fit either bulb into the wrong socket is not physically compatible due to the differing pin configurations.
The dual-filament design of the P21/5W front bulb allows it to serve more than one lighting function from a single unit. The 5-watt filament is typically used for a running or parking light function, while the 21-watt filament handles the turn signal flash, which is a common arrangement in motorcycle front signal assemblies.