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We should first explain two properties of pickups which were never previously discussed -
The rightmost columns "Output" and "Hum Canceling" will be discussed later.
Combination number 1 is the way in which guitar pickups have been manufactured and installed ever since the very first electric guitar. This was (and still is), a pretty good way to wire guitars with the only problem being hum.
Combination 2 Opposite Magnetic Polarity Opposite Coil Windings Probably the most successful attempt in reducing pickup noise was in 1955 when Gibson Guitar employee Seth Lover developed the humbucking pickup. These pickups are actually two side by side, single coil pickups with each coil differing from the other by having reverse winding and reverse magnetic polarity (abbreviated as "RWRP"). Humbucking pickups can have more than one magnet, but to keep things simple, let's see how a single magnet humbucker works. Did you notice that the magnet in the drawing has its polarity on its edges instead of on its ends? This is done to keep the magnetic strength constant from one end of the magnet to the other permitting all 6 guitar strings to have the same volume.
The other reason for polarizing the edges is to allow both coils
to have opposite magnetic polarities
which the diagram below easily demonstrates.
Moving on to the coils, both are shown with windings going in a clockwise direction. However, shouldn't those coil windings be the reverse of each other? Not exactly. Basically the term "reverse winding", although it is used by just about everybody, is inaccurate. Actually, it is the current flow in the two coils that travel in opposite directions. In the diagram, the current begins at the center of coil 1 then travels clockwise until it reaches the series connection (the place where the two coils join - indicated by the blue arrow). The current enters coil 2 at point C and if we follow it to point D, we see that the current has traveled in a counter-clockwise direction. This is what makes humbucking pickups work the way they do.
Unlike hum, an electric guitar's sound (the signal) is generated from the pickup's wiring and magnets.
So, when the guitar signal travels through the coils, no cancelation occurs because the coils are out of phase electrically and magnetically. Anyway, if you just wanted to learn how humbucking pickups work, you don't have to read any further. However, you might find it interesting to continue.
Why would we want to wire it in this way? Among other things, it is something to consider when you choose to add coil cut switching to the wiring.
The important features of parallel wiring are: • it produces a brighter sound than series wiring and • it is humbucking. In this wiring, the 'A' and 'C' wires are connected to '+' and to each other. The 'A' wire begins at the "START" in coil 1, and travels clockwise. The 'C' wire begins at the "FINISH" of coil 2 and travels in a counter-clockwise direction. The 'B' and 'D' wires are also connected and if we follow those wires, 'B' enters coil 1 in a counter-clockwise direction and 'D' goes from the center of coil 2 in a clockwise direction. So, as we can see, in both cases we have a reverse current flow and since we have opposite magnetic polarities, this is a properly wired humbucking circuit.
Even the Fender Guitar Company started making their guitars humbucking, but not with traditional humbucking pickups. Before the mid 1980's, if you had a single coil guitar, all its pickups had the same magnetic properties and all were connected so that the current flow in each was exactly the same. By now, you should know why this does not produce a hum-canceling circuit. (remember combination 1?) Then, around 1985, the Fender Guitar Company thought of an easy and inexpensive way to solve the hum problem by making the middle pickup in a Fender Stratocaster™ have reverse wiring and reverse polarity of the other 2 coils. This in effect "created" a humbucking pickup whenever someone selected two pickup combinations - neck and middle or middle and bridge.
Still, this left the neck and bridge pair in a non-hum-canceling status, which didn't bother too many people because the "neck and bridge" choice is not available for a standard Fender Stratocaster™.
Same Magnetic Polarity Opposite Coil Windings
Since humbucking pickups always have two coils with opposite magnetic polarities when would we be connecting two pickups with similar magnetic polarities? How about when connecting the neck and bridge pickups of a Fender Stratocaster™?  Looking at the diagram we see that connecting A to C and B to D (the typical parallel wiring method) creates a circuit in which the current flows through the coils in opposite directions, ensuring the hum will get canceled. However, we also need (but don't have) opposite magnetic polarities to counteract the electrical out of phase guitar signal. Basically, we have a circuit in which the hum and the guitar signal gets canceled. The guitar signal doesn't get 100% canceled (just as the hum doesn't get 100 % canceled either) and so the guitar signal has been reduced to a weak, thin, squawky "out of phase" sound. Actually, some people like this sound. It is used quite often in country music and produces a penetrating sound when used through distortion. It is not a sound you would want to have all the time but that's why there are switches on guitars.
 The above graphic shows a series wiring of this humbucking circuit. This one, due to its greater volume is more popular than a parallel out of phase circuit.
Opposite Magnetic Polarity Same Coil Windings
Of all four combinations, this is undoubtedly the worst of the bunch. It produces a weak guitar signal that isn't even hum canceling.
Well, now that you have become a humbucking "scholar", maybe your next guitar project will not seem so overwhelming.
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