Question: What exactly is coil tapping, out of phase, and series / parallel switching?
Answer: In the above Q & A we talked about two and four conductor wiring in humbucking guitar pickups. If you have four conductor wiring, you can take advantage of the three wiring options in your question... coil tapping, out of phase, and series / parallel switching. By using a switch (like a push-pull pot) to ground the two colored wires that you soldered together from one side of the pickup, you'll get coil tapping. This turns off one of the coils in the humbucker and lets you use it as a single coil. In reality it doesn't sound exactly like a true single coil pickup, but its really close. I usually do this to my personal guitars as I think it sounds really cool. If you have two humbuckers in your guitar and you switch the colored wires that you used for hot and ground on one of the pickups, you'll be able to get an "out of phase" sound whenever both pickups are in use. This produces a strange, but cool, nasal like tone that some people enjoy for solos. To change a humbucker from series to parallel operation, you can use a switch (like a push-pull pot) to use the two coils of a humbucker seperately, side by side, rather than in series as one powerfull pickup. This produces full, but slightly less powerful sound and can be useful for taming down a high output pickup, but the tonal change is more subtle... definitely not the radical change you get by turning off one coil when coil tapping.