Honda Motorcycle CB900C Custom Turn Signal Bulb Size
Honda Motorcycle CB900C Custom front turn signal bulbs measure 1034 in size, while rear turn signal bulbs measure P21W in size. The replacement chart covers 1980 to 1982 production years with corresponding bulb size specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Honda Motorcycle CB900C Custom uses two distinct bulb types across its turn signal positions: the 1034 for front signals and the P21W for rear signals, a split that holds across the full 1980-1982 model range.
The 1034 is an ANSI-standard bulb used primarily in the United States and Canada. It operates at 12V with a dual-filament configuration rated at 21/5W, meaning it serves two brightness levels within a single bulb.
The 1034 uses a BAY15d bayonet base. This base type features two offset pins, which physically prevents it from being inserted in the wrong orientation and distinguishes it from single-filament bayonet bases.
The 1034 is a variant of the widely available 1157 bulb. While the two share the same BAY15d base and general construction, they are not identical, and substitution between them warrants attention to wattage and voltage tolerances.
The P21W is an ECE-standard bulb, a specification used in Europe and internationally. It operates at 12V with a single filament rated at 21W, making it a dedicated signalling bulb without a secondary brightness level.
The P21W uses a BA15s bayonet base. Unlike the BAY15d base on the 1034, the BA15s has two pins at the same height, and the two base types are not interchangeable despite their similar appearance.
Because the 1034 is dual-filament and the P21W is single-filament, the front and rear turn signal sockets on the CB900C Custom are wired and physically configured for different bulb types. Swapping bulbs between positions is not supported by the specifications.
The differing standards between the front and rear bulbs, ANSI for the front and ECE for the rear, reflect a mixed-standard fitment on the CB900C Custom rather than a uniform regional specification across the motorcycle.