To add a coil tap to a 4 wire humbucker, simply ground the pair of wires marked 1. and 2.
Phase reversal switch:
The switch is an on-on DPDT switch and can be mounted on a push/push or push/pull pot.
With this circuit, the coils are always in series, but are either in or out of phase with each other.
Series Parallel switch ("Dual Sound"):
This switch is a DPDT on-on switch and can be mounted on a push/push or push/pull pot. With this circuit, the coils are always out of phase with each other, but are either in series or in parallel.