Honda Motorcycle CB400F CB-1 Turn Signal Bulb Size
Honda Motorcycle CB400F CB-1 front and rear turn signal bulbs use a P21W size. The replacement chart covers 1989 to 1990 vehicle production years with bulb size specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The P21W is the sole bulb type across all listed positions and model years for the Honda Motorcycle CB400F CB-1, covering both front and rear turn signals for 1989-1990.
The P21W operates at 12 volts with a 21-watt output, classifying it as a single-filament bulb intended for signalling functions rather than illumination.
A single-filament design means the P21W produces one fixed light output with no separate intensity levels, which is standard for turn signal applications where only a flashing on/off state is required.
The P21W uses a BA15s bayonet base, where "BA15s" denotes a single-contact bayonet fitting with a 15mm base width. The single-contact construction corresponds directly to the bulb's single-filament configuration.
The P21W is governed by ECE regulations, a standards framework recognized across Europe and numerous other markets worldwide, meaning the bulb conforms to internationally defined output and safety criteria.
Because the front and rear turn signal positions share the same P21W specification for 1989-1990, the bulb is physically interchangeable between those positions on the CB400F CB-1.