1. ¾Wide Circuits TestCircuit Tester for 6V / 12V/ 24V DC Systems Long Probe Continuity Tester. This probe pen is ideal for checking circuits, fuses, switches and wiring on automobiles, trailers, boats, motorcycles and other low voltage systems. 2. ¾Premium Quality The handle of the tester is made of AS plastic and the hardened tempered carbon steel probe is chrome plated. The sharp steel probe easily pierces wire insulation to check circuitry. 3. ¾FunctionUsed to Detect Power, Ground and find Shorts and Breaks in Wires. Quickly check automotive headlights, taillights, turn circuits, faulty sockets, connections, fuses, broken wires and more. Light in handle glows when circuit connection is complete, and this 3 Watt Bulb is replaceable. 4. ¾MethodBy connecting the flying lead to an earth (ground) reference and touching the screwdriver tip to various points in the circuit, the presence or absence of voltage at each point can be determined. Connect the alligator clamp to the ground, then take the probe to test circuit. If the indicator light is on, there is electricity.