An alternator and starter tester system is provided that includes a protective hood or cover, a controller connecting an LCD touch-screen, an alternator main harness connector, a starter harness self-test connector, a barcode connector, USB host and USB function connectors, an Ethernet connector, and a compact flash connector. A multiplexer is also provided to reduce the number of connectors required for various alternators that have the same type of connections but have signals on different pins.