BMW Motorcycle K100 front and rear turn signal bulbs use P21W size specifications. The replacement chart covers 1983 to 1986 production years with corresponding bulb size data.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The BMW Motorcycle K100 uses the P21W bulb type across all listed turn signal positions for model years 1983-1986.
The P21W is an ECE-standardized bulb, meaning it conforms to the Economic Commission for Europe lighting regulations used in European and worldwide automotive applications.
P21W bulbs operate on a 12-volt electrical system and draw 21 watts, which is the standard wattage for dedicated turn signal applications in this class of vehicle.
The P21W is a single-filament bulb, distinguishing it from dual-filament variants such as the P21/5W, which serves combined stop and tail light functions. The single-filament design is suited exclusively for signalling duty.
The BA15s bayonet base on the P21W features a single contact pin, in contrast to the BA15d base found on dual-filament bulbs. These two base types are not interchangeable despite sharing the same 15mm bayonet collar width.
Both the front and rear turn signal positions on the K100 share the same P21W specification across all listed years, meaning a single bulb type serves all four turn signal sockets on the motorcycle.