ON PICKUP POLARITY...

Pickup polarity refers to two things at the same time - direction of pickup windings (clockwise or counter clockwise) and magnet polarity (North facing up or South facing up).

If you are using only one pickup considerations for polarity are unimportant, as the signal is only coming from one source.  It is when you combine two or more pickups that an understanding of pickup polarity comes in handy and will help you make the best choice when shopping for pickups.

The Telecaster will be our example guitar circuit since A) it is very common and B) it is very simple as a two single coil pickup guitar.  

On a Tele the bridge pickup will be "Normal Wound, Normal Polarity."  This means that the pickup magnet faces north (the top side of the pickup) and that the winds are made clockwise from start to finish.  In nearly all single coil pickups the beginning of a coil wire is connected to ground and the end of the coil is connected to "positive" - usually a switch, volume potentiometer or output jack. More on that in just a minute.

Now when a second pickup is added to the equation we have a chance to eliminate a lot of noise or a lot of TONE.  If we used the same "Normal Wound, Normal Polarity" pickup in the neck as in the bridge, we will lose a LOT of TONE.  This is because that in two different positions of the same vibrating string the shape of that vibration is in fact completely different.  When the two signals are added together the common signals cancel each other out and you lose an incredible amount of bandwidth from your guitar, with near total removal of the largest transients and fundamental tones.  

With a "Reverse Wound, Reverse Polarity" second pickup, the opposite happens - the common signals combine for more tone, and noise is cancelled out.  IT IS TRUE, you could simply reverse the positive and ground connections for the pickup to achieve reverse polarity, but you are not realizing the full potential of these noise cancelling dynamics with the magnetic fields themselves.

A very similar methodology of mixing coils for noise rejection was adapted into the famous humbucker style pickup, perhaps even more prevalent than single coils today.  We'll broach that subject next time in "Pickup Polarity 2: Electric Humbugaloo"