BMW Motorcycle K100RT high beam and low beam headlight bulbs both use 9003 size. The replacement chart covers 1985 to 1988 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 K100RT uses the 9003 bulb size for both high beam and low beam headlight positions across all listed model years, spanning 1985-1988.
The 9003 is an ANSI-standardized bulb designation used in the United States and Canada, making it a regionally defined specification rather than a universal one.
The 9003 is a dual-filament halogen bulb, meaning a single bulb unit contains two separate filaments, one serving the high beam function and one serving the low beam function.
Because the 9003 handles both beam functions within one bulb, the BMW Motorcycle K100RT uses the same part number regardless of whether the high beam or low beam position is being referenced.
The 9003 operates on a 12-volt electrical system and carries a wattage rating of 60W on the high beam filament and 55W on the low beam filament.
The base type for the 9003 is P43t, a standardized bayonet-style base with a 43mm collar, which determines physical fitment into the headlight housing.
The 9003 bulb is electrically and physically equivalent to the H4 bulb designation used in international markets, though the two designations originate from different standards bodies and packaging may differ.