How a Starter Motor works

Detailed explanation of how a starter motor works and I open one up to take a closer look at the components inside the motor.

The starter motor is earthed to the engine (-) and connected to the positive terminal of the battery (+) via the starter relay. When you turn your key to switch on the ignition and then press the starter button to supply power to the electromagnet that makes up the starter relay and the relay completes a circuit to allow current to flow from the battery to the starter motor. The starter motor in turn is itself an electromagnet. The splines on the starter motor output shaft engage with gears that act on the crank shaft to crank the engine over and get it running at which point we release pressure on the starter button breaking the circuit supplying power to the starter motor and it stops working.