A multimeter is one of the most useful tools for troubleshooting or installing a car audio system. The picture below shows a generic multimeter. Most meters have a rotary selector switch but a few have pushbuttons to select the desired function. The meter below has a rotary selector switch. You should also notice that it has four terminals (below the selector switch) in which you place the leads.
Measuring DC Voltage
Measuring Resistance and Continuity
Measuring Amperage:
Most hand held amp meters have 2 ranges. The high range is generally limited to 10 amps. The low range is usually limited to less than one amp. Both ranges usually require moving at least one of the meter's leads. When measuring current, the meter is inserted in the circuit path. When the meter leads are in place to measure current, you must be careful NOT to connect the meter leads ACROSS any source of power. Most meters have internal fuses in the current measuring circuits for protection but you should still be careful.
Measuring DC Resistance of a Speaker:
The demo below explains how you measure the impedance/resistance of a speaker with a DMM. Actually, you're measuring the DC resistance of the voice coil. Since the DC resistance is very close to the speaker's rated impedance, you can determine the speaker's rated impedance.
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