The headlight bulb is the source of low and high beam light: two filaments of different brightness are switched from the handlebar.
Replace it if one of the filaments has burned out or the light has become dim. Before buying, check the base type, the 12 V voltage and the wattage against the previous bulb. Do not touch the bulb with your fingers. When replacing, also inspect the neighboring parts of the assembly: they wear out together.
