Unique test instrument is designed to cut the time and hassle of circuit troubleshooting. The LED reveals at a glance whether a circuit is positive, negative or open - without switching connections. The unit can activate electrical components without jumper leads or isolate bad ground contacts with- out time-consuming voltage drop tests. Follow and locate short circuits withou t wasting fuses. An auxiliary lead makes continuity testing a snap. Powered by the vehicles battery via a 20 foot cable, it works on circuits from 6-24 VDC. Short-circuit protected. Instruction book is included.