The Cal-Van Tools Logic Light Circuit Tester, No. 81, features an internal power source that allows for testing the continuity of live and non-live circuits in 6V, 12V, and 24V DC systems. It's simple to use and has patented LED edge-lighting to clearly distinguish power or ground. Illumination is red once the power is detected and green when grounded. It's ideal for testing for poor grounding, broken wires, and blown fuses. The tester creates less draw than traditional test lights with incandescent bulbs, protecting the vehicle's electrical system, the company says.