1. Autos
Send to a Friend via Email

Your suggestion is on its way!

An email with a link to:

http://autorepair.about.com/od/troubleshooting/ss/TS-circuit-tstr.htm

was emailed to:

Thanks for sharing About.com with others!

How To Test a Circuit Using a Test Light

By

1 of 2

Testing For Voltage (Positive) With a Test Light
Testing your tester on the battery.

Attach one end to ground and the other end to the positive you want to test.

photo by Matt Wright, 2008
A test light is a simple but extrememly useful tool. If you are trying to diagnose and troubleshoot an electrical problem, sometimes a test light can help you rule out possible causes much more quickly and easily than a DMM (Digital Multi Meter). It's quick, easy and very versatile, so the test light style of circuit tester can be a lifesaver. You can use it to check any positive circuit. Headlights not coming on? if the fuse is good, you can use a circuit tester to trace the wiring path and find out what's gone wrong. If the positive path is intact, you can also use the test light to check the grounding points of the circuit.

The test light is easy to use. First, let's look at how to test a positive circuit for voltage. The basic principle is illustrated in the photo above. You have a positive power source (in the case of the photo it's the battery) and you have a ground (any exposed metal that's bolted to the chassis). The test light is the go-between. If you connect one end to the positive power source and the other end to a good ground, it lights up. To test for positive voltage, attach one end to a known ground, and touch the other end to the wire you want to test. If it lights up, you're good.

Tips:

  • Before you test a circuit for voltage, be sure your test light is in good order by testing it on the car's battery.
  • The leads of the test light are reversible. It doesn't matter which one goes on the positive and which goes on the ground. Use whichever end makes your job the easiest.
  • Most test lights are very sharp on the pointed end. You can use this sharp point to pierce the plastic insulation on a wire. This means that you can test the circuit without disconnecting anything.
  1. About.com
  2. Autos
  3. Auto Repair
  4. Troubleshooting
  5. How To Use a Test Light - Using a Circuit Tester to Troubleshoot Electrical - Ground Check Circuit Test

©2014 About.com. All rights reserved.