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# Wiring Fundamentals: LED Test Light

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## LED Test Light

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 00:00 - The next automotive electrical tool we'll look at is the test light. 00:03 This is a lot like a multimeter in that it can tell you whether a voltage is present, but it can't tell you the level of voltage that's present. 00:09 And this might initially seem like a bit of a limitation. 00:12 However when we're testing or diagnosing an automotive electrical fault, we usually only find two different problems, 12 volts, where you expect to find zero volts, or zero volts where you expect to find 12 volts. 00:24 And the LED test light gives us enough information to determine this. 00:28 Like a multimeter, a test light has two probes, a positive, and a negative. 00:32 To perform a test we apply the negative probe to the ground circuit of the vehicle so that's either the battery negative or the vehicle chassis. 00:39 We then touch the positive probe to the point we wish to test. 00:43 And if a voltage is present, the LED will light up. 00:47 We can reverse the orientation of these two probes so if we touch the negative probe to the positive voltage and touch the positive probe to the ground circuit of the vehicle, we can see the other LED on the test light will light up. 00:59 This tells us that a voltage is present but it might be in the opposite direction to what we expect. 01:04 When you get to the stage of confirming the design and testing the functionality of the power supply section of your wiring harness design, and LED test light is an invaluable tool. 01:14 When you're purchasing a test light there are two common types, incandescent and LED and it's important that you select an LED test light as we can use them to test the output of a pulsed circuit such as an injector or a boost control solenoid. 01:29 To demonstrate this function we've performed a simple test on a boost control circuit.