Honda Motorcycle Grom 125 front turn signal bulbs use P21/5W size while rear turn signal bulbs use P21W size. The replacement chart covers 2014 to 2020 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 Grom 125 uses two distinct bulb types across its turn signal positions: the P21/5W for the front and the P21W for the rear, both conforming to ECE standards recognized in Europe and worldwide.
The P21/5W is a dual-filament bulb rated at 12V with a 21W main filament and a 5W secondary filament, mounted on a BAY15d bayonet base.
The P21W is a single-filament bulb rated at 12V and 21W, mounted on a BA15s bayonet base.
The BAY15d base of the P21/5W and the BA15s base of the P21W are physically incompatible with each other, meaning the front and rear turn signal bulbs are not interchangeable.
The dual-filament design of the P21/5W allows it to serve two electrical functions within a single housing, which is a common arrangement in front turn signal assemblies that also carry a parking or position light function.
The front turn signal of the Honda Motorcycle Grom 125 uses the P21/5W across the 2014-2015 and 2017-2020 model years.
The rear turn signal uses the P21W across the same 2014-2015 and 2017-2020 model years.
Because the P21W carries only a single filament, it is dedicated solely to the turn signal function at the rear position, with no secondary lighting role within the same bulb.