Mechanics

Test Light Instructions

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Step by step guide on how to use an automotive test light, information pertains to all 12 volt vehicles.

Difficulty Scale: 2 of 10

Step 1 - A test light is needed to perform electrical power and ground testing to facilitate automotive repairs, this tool is easy to use and is reasonable priced.


Test Light

Step 2 - Before staring any testing the test light itself must be tested, connect the clip or clamp to a known ground source, in this case the battery negative terminal is being used but almost any metal surface on the vehicle will work. Gently, touch the test light probe to a known power source, we use the battery positive is this example but any known power source such as a fuse or positive battery cable will work.


Testing the Test Light

Step 3 - Once the test light is properly grounded, it can be used to test not only fuse condition by touching each side of the fuse, it also confirms power at the fuse. If an accessory has failed such as brake lights and the fuse tests okay, testing can then proceed further down the circuit such as the brake light switch and so on, a wiring schematic is useful when performing these tests.


Test Fuse Power

Step 4 - When power tests okay for power at the source such as a relay or fuse, yet power is not present at a particular accessory such as the cooling fan a test light can trace the problem down through a process of elimination.


Burned Wiring

Step 5 - Power must be present at the large terminal of the alternator to charge, a test light performs this task easily.


Alternator Power

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AUTHOR


Written by
Co-Founder and CEO of 2CarPros.com
35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


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Article first published (Updated 2014-08-04)