Abstract: An improved alternator/starter testing device includes an electronic voltage regulator for regulating the output of an externally regulated alternator. A selectable load switch allows so-called "high output" alternators to be tested without damaging the voltage regulator. For certain types of internally regulated alternators, the testing device includes a meter disconnect circuit, coupled to an "energize" switch in the testing device, which operates to disconnect the testing meter during a period in which the energize switch is temporarily depressed to supply power to an internally regulated alternator under test, thus preventing misleading test results if a defective alternator is tested. Internal thermal circuit breakers are provided at strategic locations in the testing device to prevent internal circuit damage due to defective alternators and starters.