Neilsen Auto Circuit Wire Tracing Short Open Finder Voltage Tracer & Detector Auto Circuit Tracer and Detector Auto Circuit Tracer and Detector Find short and open circuits fast and easily. Designed to identify and trace wires or cables without damaging the insulation - you just simply attach the sender unit to the circuit and follow the wires using the flexible detector. Checking for Short Circuits Locating Open Circuits Battery Voltage Indicator Range of measurement - 6 - 42V DC 2 x 9V batteries ( Not Supplied ).