Re: What is phasing?
I'll try to keep this simple:
A guitar pickup generates an AC voltage when a string vibrates above it.
AC means that the voltage goes positive, then negative, at the frequency of the note. If you combine the output of two pickups, and they're "in-phase", it means that both voltages are going positive at the same time. If they're out-of-phase, one is going positive, while the other goes negative. These two signals would, of course, cancel each other out. But since they aren't identical, the cancellation won't be 100%, and thus you'll get a tiny bit of the signal through. The "difference" between the two p'ups, to be exact. This will be a very weak and hollow sound.
Parallel just means that the "plus" terminal of one p'up is connected to the "plus" of the other. Same for the grounds, so they operate beside, or parallel, to each other.
Series means that only one p'up is grounded, its "plus" goes to the "minus" of the other, and its "plus" goes to the output jack. So the two p'ups are in-line with each other. This just gives a different tone.
Parallel wiring is more or less "conventional" on a twin pickup guitar.
Generally, guitar pots come in two values, 250k, (250,000 ohms), for single coils, and 500k for humbuckers. Active pickups often use 25k pots.
