BMW Motorcycle K1 front and rear turn signal bulbs utilize a P21W size across all applications. The replacement chart covers 1988 to 1993 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 BMW Motorcycle K1 uses the P21W bulb for both front and rear turn signals across all listed model years, 1988-1993.
The P21W is an ECE-standard single-filament bulb rated at 12 volts and 21 watts, mounted on a BA15s bayonet base.
The BA15s designation refers to a single-contact bayonet base with a 15mm collar, which positions and locks the bulb with a twist-and-push motion.
Because the P21W is a single-filament design, it serves a dedicated signalling function rather than a combined stop-and-signal role.
The ECE standard classification indicates the P21W is recognized for road use across European and many worldwide markets, reflecting a regulated output and base specification.
The identical P21W fitment across both the front and rear positions on the BMW Motorcycle K1 means a single bulb type covers all four turn signal sockets on the motorcycle.
The BA15s base is a single-contact variant, distinct from the BA15d double-contact base; substituting a BA15d bulb in a BA15s socket is not electrically compatible.
At 21 watts, the P21W draws a defined current load that the turn signal flasher relay on the K1 is calibrated to recognize; substituting a bulb of a significantly different wattage can cause incorrect flash rates.