An alternator tester is provided for testing an alternator of a vehicle while the alternator is coupled to the vehicle. A sensor is configured to couple to the vehicle and sense a signal related to operation of the alternator. A memory contains data related to operator instructions for performing an alternator tester of a function of vehicle type. A processor configured to provide an output indication of alternator condition based upon the sensed signal. An extra load or connection can be provided for coupling to the electrical system.