What is the primary function of a starter solenoid?

The primary function of a starter solenoid is to engage the starter motor. When the ignition key is turned or the start button is pressed, electrical current flows through the solenoid, which acts as a high-current relay. This action closes the circuit and allows battery power to flow from the battery to the starter motor. As a result, the starter motor engages the engine's flywheel, initiating the engine's operation.

In contrast, the other options do not describe the role of the starter solenoid. Charging the battery is a function of the alternator and the charging system, not the solenoid. Regulating voltage is typically a function associated with the voltage regulator, which ensures that the electrical system receives a steady voltage. Providing power to the alternator is not a responsibility of the solenoid, as the alternator functions independently once the engine is running. The primary task of the solenoid remains centered on engaging the starter motor, which is vital for starting the engine.