Abstract: A diagnostic tester for use with a lighting system having at least one lamp, a ballast, a capacitor, and a plurality of wires interconnecting the lamp, ballast, and capacitor. A diagnostic receptacle is electrically coupled to the lamp, ballast, and capacitor. A connector is adapted to engage the diagnostic receptacle and provide an electrical connection therewith. The connector is electrically coupled to circuits for testing the ballast, the capacitor, and the plurality of wires in the lighting system. An indicator is provided for separately indicating whether the ballast, the capacitor, and the plurality of wires are functioning properly. An indicator may also be employed with a pair of terminals on the tester housing for testing the continuity of a lighting system fuse.