Starter solenoid

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A starter solenoid is an electromagnet which is actuated to engage the starter motor of an internal combustion engine. It is normally attached directly to the starter motor which it controls.

Its primary function is as the actuating coil of a contactor (a relay designed for large electric currents) which connects the battery to the starter motor proper.

All modern cars also use the starter solenoid to move the starter pinion into engagement with the ring gear of the engine.

The starter solenoid is sometimes called the starter relay, but many cars reserve that name for a separate relay which supplies power to the starter solenoid. In these cases, the ignition switch energizes the starter relay, which energizes the starter solenoid, which energizes the starter motor.