A check for short circuits is one of the most basic tests you can perform with a multimeter. On the simplest meters, you use the resistance setting; sophisticated models have a continuity setting that flashes a light or beeps a tone to let you know a connection is a short circuit.
Turn Off Power
Turn off all power to the circuit or device under test. Unplug the equipment from the AC outlet.
Probing an electrical circuit with a multimeter may pose a dangerous shock hazard if the circuit's power is on.
Set Multimeter to Resistance or Continuity
Switch the multimeter on and turn its selector knob to the resistance setting. Use the continuity setting if your meter has that function.
Some multimeters may have several resistance settings; choose the lowest resistance scale on the meter.
Touch Probe Tips Together
Touch the test probes together and observe that the resistance reading goes to nearly zero. For continuity, the light flashes or a tone sounds.
Locate Circuit Component
Locate the component or portion of the circuit you want to check for a short. The tested part should not normally have zero electrical resistance; for example, the input of an audio amplifier should have a resistance of at least several hundred ohms.
Touch Probe Tips to Circuit
Touch the metal tip of the black probe to the circuit’s chassis or electrical ground, and touch the tip of the red probe to the parts of the circuit you suspect may have a short. The tips of the probes must touch metal parts of the circuit, such as a component lead, circuit board foil or wire.
Observe Meter Display
Observe what the meter does when you touch the probes to the circuit. A high resistance signifies an open circuit. Very low resistance -- about 2 ohms or less -- indicates a short circuit. A meter with a continuity setting flashes or beeps only if it detects a short circuit.
Some meters may indicate an open circuit as "overload" or infinite resistance.
Chicago native John Papiewski has a physics degree and has been writing since 1991. He has contributed to "Foresight Update," a nanotechnology newsletter from the Foresight Institute. He also contributed to the book, "Nanotechnology: Molecular Speculations on Global Abundance."