Starter motors come in either standard, high-torque or gear reduction models. The primary purpose is to turn the engine over in order for ignition to commence and the engine to start. The starter will always need to engage the flywheel on the rear of the engine in order to turn the engine. The flywheel is a large wheel with teeth around the circumference and is attached to the rear of the crankshaft. Generally the starter will be installed on either bottom-side of the engine with the gear end facing rearward toward the flywheel. Some vehicles have the starter attached to the top rear of the engine under the intake manifold.
The starter is an electric, high-torque motor with a gear that rides on a spiracle shaft on the end. This spiracle shaft is called the bendix. When the starter motor is activated, the gear on the shaft spins at a high speed and the spiracle shaft causes the gear to wind its way up the shaft extending it out to engage with the flywheel. When the starter is deactivated, a spring pulls the bendix back in toward the starter, disengaging it from the flywheel.
The wiring for a starter is consistent with most all vehicles with the exception of the security system intervention. The main power for the starter motor runs directly from the battery or battery source to the top post of the solenoid on the starter. In some cases the starter will have a separate solenoid located on the fender well. The solenoid is just a remotely activated switch to turn the starter on and off. If it is a remote solenoid on the fender well there will be two large terminals--one on each side of the solenoid--and two small terminals in the center of the solenoid.
The large diameter power wire from the battery is attached to one of the large terminals and the other large terminal goes to the starter. The small terminals are marked 'S' and 'I.' The S terminal is for a wire from the ignition switch that is activated when the key is turned to the start position. When this terminal is activated, the solenoid closes the circuit to the starter and activates it. When the key is released, the circuit is open and disengages the starter. The same thing applies with a starter-mounted solenoid.
