Abstract: Electrical power for an electrically heated vehicle windshield is controlled by an arrangement utilizing a modified alternator coupled to the windshield heater via an autotransformer. In a high power mode, the vehicle battery is coupled to a center tap of the alternator, while in a normal power mode the vehicle battery is coupled to a conventional rectified output of the alternator. A microprocessor controlled silicon controlled rectifier bridge provides direct current to the windshield heater element by rectifying the output of the autotransformer. Additionally, a current sensor coupled to the heater element is utilized by the microprocessor to determine the electrical resistance of the heater element in order to take required diagnostic measures.