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Most factory wired CCars utilize a system of contactors to control motor speed and direction. A series/parallel contactor and a bypass relay control speed while a taller forward/reverse contactor handles more direction and a safety "neutral" position. These contactors control all the power to the motor and, even worse, must do this by opening and closing mechanical contacts under load. Motor current can be in excess of several hundred amps during locked rotor (another way of saying the motor is not turning yet). In order to minimize arcing/sparking at the contacts the contactors are energized ..