The heart of an electric guitar's tone is in its pickups. While measuring the resistance of a pickup won't tell you much about its sonic characteristics, it will establish a ballpark estimate of how “hot” the pickup will sound, and whether it's in good working order.
Place the pickup on a flat surface and anchor its lead wires with tape. If the pickup has more than two lead wires and you have trouble identifying which you should meter, trace the wires back to the pickup: The wires that directly contact the pickup windings are the only ones that will give you the pickup's resistance.
Set your volt-ohm meter to “Ohms” or “Resistance.” If you have the option of several ranges of resistance, choose “20 kOhms.” Most single-coil guitar pickups have under 10 kilo-ohms of resistance, and most humbuckers (double-coil pickups) have under 20 kilo-ohms.
If you have an analog meter, it is necessary to establish a zero reading. Hold the meter's red and black probes together and turn the “Zero Ohm Adjust” knob until the meter reads “0.” Digital meters do not need to be zeroed.
Touch the meter's black probe to the bare wire at the end of the negative pickup lead, usually the black wire.
Touch the meter's red probe to the positive lead, usually red or yellow.
Do not touch any conductive metal, either the probes or the pickup leads, with your fingers. Doing so will measure your body's resistance and skew your results.
Watch the meter's needle or digital readout. An analog meter's needle will take a moment to settle on the correct reading, but a digital meter will give immediate results. The higher the resistance, the hotter the pickup will sound. If there is no reading, the pickup may be damaged.
Be careful not to touch the pickup winding wires. These windings are made of very thin gauge wire wound thousands of times and are thus very fragile. Breaking them will totally disable your pickup.