[rotorwrench]

A diode is like a one way check valve in a hydraulic system. It allows the current to pass in one direction only. They are generally made in a way that you can tell which direction it should be installed in the circuit. They can go south on you too. When they do, they can open the circuit completely or allow some current to flow both ways. An alternator has a whole bridge of them mounted inside for the same purpose as the cut out but it also has to bridge the current from AC to DC so that it will work in a motor vehicle.