An alternator test apparatus includes a processor and solenoid drivers for controlling solenoids to selectively switch three discrete, fixed-resistance loads and combinations thereof in parallel across the battery terminals, while monitoring battery output voltage and alternator output current. The system automatically sequentially increases the load from zero to a maximum load and stores the maximum alternator output current and the load at which it was achieved. After application of the maximum load, the system returns to the load at which maximum alternator output was achieved and tests the alternator diode.