Solenoid Switches

The solenoid switches is the part of automobile which relays a large electric current to the starter motor. The system converts electrical energy from the batteries into mechanical energy to turn the engine over. It is mounted on the starting motor and forms the major component of the starting system. The coils inside the solenoid are energized by electricity, they create a magnetic field which attracts and pulls a plunger. Attached to one end of this plunger is a shift lever. The lever is connected to the drive pinion and clutch assembly of the starter motor.

The solenoid receives a large electric current from the car battery and a small electric current from the ignition switch. As the ignition switch is turned, a small electric current is sent to the starter solenoid. The pair of heavy contacts closes, relaying the a large electric current to the starter motor, which in turn sets the engine in motion.

Once the engine starts, the key-operated switch is turned, a spring in the solenoid assembly pulls the pinion gear away from the mesh, and the starter motor stops. The starter's pinion is clutched to its driveshaft through an overrunning sprag clutch which allows the pinion to transmit drive in only single direction. In this manner, drive is transmitted through the pinion to the flywheel ring gear.

If the power supply to the solenoid is insufficient, it will fail to start the motor and may produce a rapid clicking or clacking sound. The lack of the power may be caused by by a low or dead battery, by corroded or loose connections in the battery cable, or by a damaged positive (red) cable from the battery. Any of such problem may create resistance for the current resulting in proper transmission of the power.

To reduce the chances for such as failure, the battery connections should be cleaned and tightened at every oil change. Starting fault of the solenoid can detected at service center by a test of the car's starting, charging and battery systems.