Solenoids (is also called relays) operate by receiving both large electrical currents from battery and smaller electrical currents from the ignition system. Its primary function is as the actuating coil of a contactor (a relay designed with large electric currents) which connects the battery to the motor proper.

Solenoid / relay are used for wide applications. In automobile field, it is applied from starting the engine to shifting the transmission. Solenoid / relay are used to activate four-wheel drive system, fuel injection systems, locking the doors of the car and controlling the air flow in the vehicle's air conditioning system. Besides, Fair Sun also produces solenoid / relay for agricultural and industrial vehicles, marine and home backup portable generator.