How a test light can be used to test for power and ground?

Answer 1

Testing for 12V DC power using a 12V DC test light, clip the test lead to a known ground (preferably battery negative post) then probe with the test light tip for power. Test light will illuminate when power is touched.Testing for 12V DC ground, clip the test lead to the positive post on the battery then probe with the test light for grounds. Test light will illuminate when a ground is touched.

Answer 2

An ordinary, 'Plain Jane' test light will only test for power, but you can use it to test for ground. First, you find an adequate ground to apply the clamp to (other than the ground you're trying to test), then you probe the hot circuit. If the hot circuit is working properly, and the ground you chose is adequate, then it'll light up either red or white, depending on who made it. Once you've verified the hot circuit works and your test light does, as well, then you can apply the clamp to the wire or other ground you want to test.. if it's a plug, you might need to put a back probe to it for something to clamp onto. Then you probe the hot circuit again.. if it lights up, you've got ground in the circuit you're clamped to... if it doesn't, then you don't.

You can also use a 'logic tester' type of test light... not sure who all makes this type, but I've seen them at auto parts stores... mine was made by Mac Tools. These will have two leads - one will be marked with black for the ground, one will be marked with red for positive... you hook those to an active hot line and a good ground.. if you have a good connection, it'll show a light at the bottom to indicate this... then you probe the circuit you want to test.... a hot circuit will show a red light, a ground circuit will show a green light, and open circuit will show no light.

The other way is to use a Power Probe... you can use a cigarette lighter plug or clamp the power leads directly to a battery or other power source... it does the functions of a test light, plus it reads voltage, and it can also be used to supply power to energize a circuit (the latter makes it a little dangerous in the hands of someone lacking in experience, though, and I never loan this tool to the new mechanics in my shop).