What's the use of resistors on motorcycles?

This is called bleeder resistance (or bleeder resistance). The resistors connected in parallel at both ends of the energy storage element provide an energy consumption path for the energy storage element and make the circuit safe. It can be a diode, such as a diode with a parallel inductor (relay package).

There were many motorcycles in the early days, which mainly played the role of protecting electrical appliances and stabilizing voltage.

Generally, only classic cars will be equipped with leakage resistors, mainly because they are equipped with simple rectifiers and use less current (mostly AC headlights). The leakage resistor is installed to prevent the battery from being damaged by overcharging when the lamp is not used during the day.

When you remove the discharge resistor, you can measure the charge of the battery. If the charge is normal, it is not necessary to install it, otherwise it is necessary to install it, or try a suitable rectifier. As long as the charge is not large, it is not needed.