{"id":103149,"date":"2024-03-14T21:16:36","date_gmt":"2024-03-15T04:16:36","guid":{"rendered":"https:\/\/blogv2prod.wpenginepowered.com\/blog\/?p=103149"},"modified":"2024-08-20T00:25:40","modified_gmt":"2024-08-20T07:25:40","slug":"how-to-use-an-automotive-test-light","status":"publish","type":"post","link":"https:\/\/www.carparts.com\/blog\/how-to-use-an-automotive-test-light\/","title":{"rendered":"How to Use an Automotive Test Light"},"content":{"rendered":"\nReading Time: <\/span> 7<\/span> minutes<\/span><\/span>\n\n\n

An automotive test light or circuit tester can check the presence or absence of electricity between two locations in a vehicle. This tool is used to test load carrying electrical circuits. A 12 volt test light is a handy visual indicator that voltage is available, but can’t measure current flow higher than the test light’s own current consumption.<\/p>\n\n\n\n

Test lights for cars are composed of a handle similar to a screwdriver except that the handle is hollow with a flexible wire passing through a removable rear cap that provides a contact on the inside of the cap. Typically, there will be a spring between the bulb and the inside end of the probe, which extends like a screwdriver bit out of the handle except that it has a sharp tip.<\/p>\n\n\n\n

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There are high impedance test lights with LEDs in them that pull almost no current, and there are low impedance test lights (like the one shown) that pull about 0.25 amps.| Image Source: Richard McCuistian<\/figcaption><\/figure>\n\n\n\n

Using the tool involves clipping the wire onto a metal component like your vehicle’s chassis or your battery’s negative terminal and then using the probe to check if any electricity passes through the probe into the wire or vice versa. If there’s electricity, then a light on the probe will illuminate.<\/p>\n\n\n\n

In this article, we’ll discuss how to use a test light on a car.<\/p>\n\n\n\n

Checking for Voltage<\/h2>\n\n\n\n

Just clip the wire to a ground source, which can be your battery’s negative terminal<\/a> or your vehicle’s chassis, touch the probe to the positive battery terminal to make sure your clip connection is good and you have source voltage at the battery,  and then use the probe to check for voltage at the test point.<\/p>\n\n\n\n

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Diagram showing how to use a test light | Image Source: Richard McCuistian<\/figcaption><\/figure>\n\n\n\n

If the circuit is switched on and you don’t have voltage at the test point, you need to find out why by checking the same circuit at a point closer to the source of the voltage. When you find voltage, the open circuit is between the place that illuminated the test light and the place nearest to it that didn’t. <\/p>\n\n\n\n

In the video below, we demonstrated how all the voltage that was supposed to be leaving the battery wasn’t even making it into the battery terminal, even though the connection looked just fine. We found the problem with a test light.<\/p>\n\n\n\n

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