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# Wiring Fundamentals: Multimeter

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## Multimeter

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 00:00 - A multimeter is a completely essential tool to have in your wiring tool kit. 00:04 As the name suggests, a multimeter can be used to make multiple different measurements depending on which mode we have it set to. 00:10 Most commonly we use it to measure voltages, resistances, and confirm that we have electrical continuity between two points. 00:17 As these are all relatively basic functions, the price of a multimeter to suit our application can be quite low. 00:23 We'll look at those three most common tests performed to give you a feeling of how you would use a multimeter when you're building and testing your wiring harness. 00:30 The first measurement we'll make is a DC voltage measurement. 00:33 This will tell us the electrical potential difference between the two multimeter probes. 00:37 Now important to realise is this is only the difference in electrical potential between the two probes and it's not absolute values. 00:44 For this reason we normally connect the black multimeter probe to the ground circuit of the vehicle. 00:49 So that's either the battery negative or the vehicle chassis. 00:52 The red probe is then touched to the point we wish to measure. 00:55 To make a voltage measurement we install the black multimeter probe into the com or common port of the multimeter and we install the red multimeter probe into the volts, ohms, and milliamps port as we're making a voltage measurement. 01:07 We then turn the rotary dial to select a DC voltage measurement with a range that is closest to but still above the voltage that we expect to read. 01:15 As we're measuring the electrical system of a common automobile, we can expect our measurement to be around about 12 volts. 01:21 So we'll turn this to the 20 volt scale. 01:26 We then touch the negative lead of the multimeter to the ground circuit of the vehicle and touch the positive lead to the point we wish to measure. 01:34 In this instance we're reading a voltage of 12.33 volts across this battery so we can tell that it's fully charged. 01:40 The next measurement we're gonna make, is a resistance measurement of an injector to determine whether it's a high or low impedance injector. 01:47 To make this measurement we ensure that the black lead of the multimeter is in the common port and the red lead is in the volts, ohms, milliamps port, as we're making a resistance measurement and this is in ohms. 01:57 We then turn the rotary dial to the resistance section, and select a scale that is closest to but still above the resistance we expect to measure. 02:06 In this case we select the 200 ohms scale as we know the resistance of our injector will be below this value. 02:13 We then touch the multimeter probes to either electrical terminal of the injector. 02:21 And we can see a resistance measurement of 12.5 ohms, meaning this is a high impedance injector. 02:28 The next test we'll perform is an electrical continuity test. 02:30 This is just another form of resistance test but the multimeter will provide us with an audible tone to tell us whether the two points we're testing are connected electrically. 02:40 To make this test we select the electrical continuity mode of the multimeter and we ensure that our multimeter leads are installed in the common and volts, ohms, milliamps ports. 02:50 We then touch the two probes to the points we wish to determine whether or not are connected electrically and if they are, the multimeter will provide us with an audible tone. 03:01 This can be really handy as it means we can perform this test without needing to take our eyes off our work. 03:06 Particularly with the continuity function, you want to test this on the multimeter before you purchase one. 03:11 I found several multimeters out there that have a noticeable delay between touching the two probes together and the audible tone sounding. 03:17 This can become a real pest when you're trying to find either end of a wire at opposite ends of a wiring loom. 03:23 Many multimeters you'll find on the market won't have manually selectable ranges. 03:26 These are called auto ranging multimeters and they automatically adjust as you're making the measurement. 03:32 This sounds great in theory but I find it produces a noticeable delay when you're taking the measurement and can actually be a bit of a hinderance. 03:38 For this reason, I like to use a much cheaper multimeter that has a manually selectable range. 03:43 Any multimeter you find on the market is going to have the three functions that we've talked about here, which means you can pick one up at a very decent price.

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