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How to Trace Wires Using an Ohmmeter

Georg Ohm was an early 19th century German physicist who contributed to our understanding of electricity. He is most famous for Ohm̵7;s law, which describes the relationship between voltage (the pressure that causes electrons to move), current (the number of electrons that are moving) and resistance (the opposition that a substance presents to electron flow). He also gave his name to the unit of resistance: the ohm. Because the unit of resistance is called an ohm, the meter that measures resistance is called an ohmmeter. Ohmmeters are very handy for tracing wires.

Instructions

- 1
  Identify the wires that make up a cable with an ohmmeter. Each wire in the cable has its own insulation and each single wire insulation is color coded. If there are lots of wires, these colors are not so easy to distinguish. Hold one probe of the ohmmeter to a wire at one end of the cable, then touch the other probe to each wire emerging from the other end of the cable. One of the wires will make the ohmmeter display a value near zero. This means you have the two probes on two ends of the same wire ̵2; wires have very little resistance. All the other wires will display a value close to the infinity mark on the meter.
- 2
  Turn the power off before tracing wires through an electronic device. If the device is battery-powered, take the batteries out of the device. A good place to start the trace is at one of the battery terminals ̵2; or at the place where power comes into the device. Attach one probe to the power source and move the other probe through the device ̵2; as long as there no breaks in the wires the resistance will be low. One step past a break, the resistance will be very high.
- 3
  Watch out for the effects of electric components on your trace. Coils will show a high resistance at first that slowly falls to zero. Capacitors will show very little resistance at first, but the resistance will slowly rise to infinity. Diodes show high resistance in one direction, but if you switch the probes and measure in the other direction, the resistance will be low.

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