The alternator is the electricity supply unit for the entire car. Its a very important part on your vehicle as it is responsible for keeping your battery charged which in turn supplies the car with the electricity required to function. There is a belt that attaches to the pulley which drives the alternator. The belt creates and produces electricity by converting mechanical energy into electrical energy. Anything electrical on your vehicle relies on the alternator to produce sufficient electricity to power parts such as your ignition lights, sound system, heater, wiper blades and anything else that needs electricity to run. The alternator also recharges the battery after the starter motor uses it to start the car. If you ever have starting issues with your vehicle the most common issues are related to either the battery, alternator or the starter motor.