steel probes easily pierce wire insulation to check circuits. Probe pens are great for checking circuits, fuses, switches, and wiring in cars, trailers, boats, motorcycles, and other low-voltage systems. Ground the alligator clips and test the circuit with the probe. If the light comes on, there is power. Conversely, the point under test there is a fault, to be investigated 1.2M Spring Cable: The cable is extensible to use and the total length is 1.2M, which can meet your most needs. 1. Hold the alligator clip of the measuring to the ground wire (such as the metal or negative pole of the car) 2. to measure the of the electric pen needle contact to test the conductive metal in the circuit 3. If the light bulb of the stylus will light up, it means that the point under test has constituted a circuit and is working properly. Measuring ranges: 6-12-24 V Colour:Photo Color Material:plastic Package Contents: 4 x Circuit Tester Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.