BMW Motorcycle K100LT front and rear turn signal bulbs use a P21W size. The replacement chart covers 1987 to 1992 production years with 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 K100LT uses the P21W bulb type for both its front and rear turn signals across all listed model years, spanning 1987-1992.
The P21W is an ECE-standard bulb, meaning it conforms to the Economic Commission for Europe's lighting regulations, which are widely adopted across European and international markets.
P21W bulbs operate at 12 volts and consume 21 watts, which is the standard wattage for single-filament automotive signalling applications.
The P21W uses a BA15s bayonet base, where "BA" denotes a bayonet-style fitting, "15" refers to the 15mm base width, and the lowercase "s" indicates a single-contact configuration.
Because the P21W is single-filament, it serves one lighting function per bulb, which is why separate units are specified for the turn signal role rather than a dual-filament type that might combine functions such as braking and signalling.
The BA15s base is not interchangeable with the BA15d base, which carries two contacts. Substituting a BA15d bulb in a BA15s socket would result in an incorrect fit.
The front and rear turn signal positions on the K100LT share the same P21W specification for all listed years, meaning both positions draw from the same bulb type.