Use this heavy duty circuit tester with retractable wire to check all 6 and 12 volt circuits and accessories including lights, starters, cooling and heating components, radios, and relays. Not recommended for use on computers, sensors, or computer wiring. The retractable wire stretches uo tp 12' to make testing easy and is equipped with a spring supported strain relief. The tester has a super sharp probe and heavy duty ground clip and insulator. Simply clip onto one end of the circuit - stick your probe on the other end and if it is complete, the handle lights up. It doesn't get much easier.