Honda Motorcycle ST1100 front turn signal bulbs use 1034 size while rear turn signal bulbs use P21W or 1073 size. The replacement chart covers 1991 to 2003 vehicle 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 ST1100 uses the 1034 bulb across all front turn signal positions for every model year in the specifications, spanning 1991-2003.
The 1034 is an ANSI-standard dual-filament bulb rated at 12V and 21/5W, fitted with a BAY15d bayonet base, and is classified as a variant of the 1157.
Because the 1034 carries a BAY15d base, it is not interchangeable with single-filament bulbs that use a BA15s base, such as the P21W or 1073, without a socket adapter.
The rear turn signal position on the ST1100 does not use a single bulb type across all years. Instead, the specifications show alternating fitment between the P21W and the 1073 depending on the model year.
The P21W is an ECE-standard single-filament signalling bulb rated at 12V and 21W, fitted with a BA15s bayonet base, and is common in European and worldwide markets.
The 1073 is an ANSI-standard single-filament bulb rated at 12V and 13W, also fitted with a BA15s bayonet base, and is described as a lower wattage variant of the 1156.
Although the P21W and 1073 share the same BA15s base type, their wattage ratings differ at 21W and 13W respectively, which means substituting one for the other affects light output.
The rear turn signal on the Honda Motorcycle ST1100 uses the 1073 in 1992, 1995, 1997, and 2002, while the P21W is specified for all remaining years covered in the data.
The front and rear turn signal positions on the ST1100 require different bulb bases throughout the entire model range, as the front uses a BAY15d socket and the rear uses a BA15s socket.
The ANSI and ECE standards represented in these specifications reflect regional market differences, with ANSI designations such as 1034 and 1073 associated with North American fitment and the P21W designation associated with international markets.