How to check polarity on pickups
with an ohm meter prior to installation.

This process is most easily done with an analog meter with a needle.
It is possible to do with a digital but the effect is not as obvious.
1: Connect each end of the lead to the appropriate side of the meter.
i.e. The red will be connected to your hot and the black to your ground
(If the pickup is installed in the guitar simply plug in your cord and use the
tip as hot and the sleeve as ground or unscrew the casing around the
jack to access the hot and ground.)

2: Using a piece of steel or a screw driver let it attract to the top of the pickup
you are testing and lay flat on the magnets or poles. Be careful not to scratch
your covers!

3: Look at the meter and take a mental note of the reading. Pull the screwdriver or
steel away from the pickup. The pickup will induct either a positive or negative
current. The numbers on the meter will move either up or down. Remember
this movement.

4: Connect the meter leads to the pickup you are trying to phase to the mate.
Repeat the process above.

5: IF the meter reacts in the same direction to both pickups they are in phase
and you can proceed with installation.

6: IF the meter reacts in the opposite direction you will need to either swap the
electrical polarity by installing the pickup with the leads in the opposite direction
you have tested or change the magnetic polarity if possible.
NOTE: Some pickups like Telecasters with grounded metal covers and baseplates
or humbuckers with a Gibson style shielded lead will need the magnetic polarity
reversed for this to be effective. Not doing so can result in the hot signal going to ground.