A lot of farmers buy a voltmeter but never gain confidence in how to use it. Here are the basics:
Plug the red test lead into the “positive” test port. Plug the black test lead into the negative/ground port. Locate the Direct Current (DC) setting, usually identified by a “DC” logo and a solid line over a dashed line. (The Alternating Current (AC) setting, identified by “AC” and a wavy line, is for household current.) Find a 12-volt battery. Touch the red/positive test lead to the positive battery terminal. Touch the black/negative lead to the ground terminal on the battery. The meter will read 12 volts, or something close that, depending on the charge of the battery.
And that’s the basic idea. As long as the negative test lead is touching either the battery’s negative terminal or the engine’s frame, you can touch the positive test lead to any current-carrying wire to see how many volts it’s carrying.
(If you accidentally reverse the red and black test leads—no problem. The meter will simply read “-12,” indicating reversed polarity. No harm done to the meter or to the circuit being tested.)
An electrical engineer will say it’s way more complicated than that. It is, but for the purposes of learning to use a voltmeter, simply checking from a known ground to a potential source of voltage is a good start. As long as a primary, non-computerized circuit shows from 11.5 to 13.5 volts, life is good. If it doesn’t, use the voltmeter to trace backward toward the battery to determine where the voltage deficiency occurs.
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