# Question: Test Lights????

Can someone please explain to me the theory behind a test light? I bought one at a garage sale and would like to know how to use it. Im having trouble
figuring out what a good "ground" is. I was trying to test a couple fuses on my car but the light didnt seem to work. Im pretty sure its not defective.
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A test light needs a battery. It is used to test for a complete circuit. If the fuse is good the test light will glow. A good ground will make the test lamp glow any time you go metal to metal(unless the metal is not touching the car frame.".

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Well, I guess there is more than one type of "test light."
A common one used for trouble shooting automobile wiring looks like screwdriver handle with a ice pick tip. There is a wire lead with a allegator clamp that is supposed to be connected to a metal part of the chassis (with today's plastic cars, it can be difficult to find metal in the passenger compartment or even the trunk) There is a 12 volt lamp in the handle. With the lead connected to "ground" (the metal chassis) you poke about with the ice pick point to see where power is and where it ain't. Many automotive fuse holders do have any "hot" metal exposed which makes things safter but it requires you to "dig in" with the ice pick to see whether the fuse is working. The ice pick can also punch a hole in a wire to see if the conductor inside is "hot."
For household use there is the neon "tester" which is just a small neon lamp in series with a resistor. If you connect the two leads to 120 volts the lamp will glow brightly. If you hold one lead in your hand, you can use the other lead to test for "hots." When the other lead touches a hot wire, the lamp will have a dim glow.
With the "testers" with batteries, the simplest would be a continuity tester. It's like the ice pick test except that it has a 1.5 volt bulb and a 1.5 battery. If the lead touches the tip the lamp will light. It's useful for simple testing of stuff that out of the car or when the battery is disconnected. With power on, you risk turning the 1.5 volt lamp into a fuse.
There are small testers with batteries that can sense AC voltage and can also function as continuity testers. One side of the circuit is through the body of the user. These are nearly impossible to burn out and are handy to keep in your "junk drawer."
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On 11 Sep 2004 22:45:09 GMT, snipped-for-privacy@aol.com (USApoSOUL) wrote:

If this is one of the simple test lights with a lead coming off what looks like a screwdriver and a light in the handle, connect the lead to a ground in the car. This would be a screw or other piece of metal somewhere in the vicinity of where you are looking for a voltage to test.
You can check to see if you do have a good ground by checking a point on the fuse block that has voltage. If the light works, you have a good ground and can check other points to verify if a fuse is good.
You of course have to leave the fuse plugged in the fuse block to check them with this light. A good fuse would check with a light on both sides if good.
Only one side would light if the fuse is bad.
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