Multimeter do’s and don’ts

Checking truck electrical connections: Multimeter do’s and don’ts

As the spring season starts to thaw winter’s freeze, it’s a good time to give your trucks and trailers a good once-over to ensure that all components are operating properly. The lighting system is a good place to start. Check for any loose connections, broken wires or excessive corrosion at the connections, since, of course, any electrical device needs power to work. A multimeter is your go-to tool for troubleshooting a circuit or electrical device.

“Testing for direct current voltage is probably the most commonly performed diagnostic with a multimeter because the power supplied by the tractor batteries to the rest of the vehicle is direct current (DC) voltage,” explained Andrea Smeby, content specialist with Phillips Industries. “Digital multimeters that have a numeric display are the most common, but every multimeter is comprised of three key components: the display, the rotary knob or dial to select the electrical measurement setting, and ports for two detachable probes used to perform a diagnostic.”

Smeby outlined a few “Do’s and Don’ts” when using a multimeter.


  • Have a basic understanding of how electricity works. Understanding the basics of how electricity performs within the scope of the test you are performing allows for a better understanding of not only how to set the multimeter up for proper testing, but also what the results mean.
  • Make sure that the probes are plugged into the proper ports or the multimeter won’t be able to perform the test.
  • Make sure the dial or knob is set to the correct electrical unit and correct measurement range. If not set to the correct measurement range, the reading will display a 1 (one). Some advanced devices are “auto-range,” meaning after the multimeter is set to the desired unit of measure it will automatically adjusts the range for the test being performed.
  • Refer to the owner’s manual when in doubt, as most should have a wealth of knowledge regarding the use of the product.


  • Pierce the jacketing to test wires, as holes can create paths for contaminants to wick their way into the wring system, corroding wires from the inside out.

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