Very professional test tool This circuit tester can test uncertainties in the vehicle circuit. Perfectly perform each function, such as continuous testing, polarity testing, jumper operation, short-circuit tracking positioning, etc. Positive Negative Negative Test Function Electrical Tester is used to test uncertainties in the vehicle circuit, and connect the red clip to the positive electrode of the vehicle battery. Connect the black clip to the negative electrode of the battery. When the tip of the probe is in contact with the positive electrode (+), the LED should illuminate Red. Contact the tip of the probe (-), the LED should be green.