For the installation, on the FAQ page of the main BKP site:
What is four conductor wiring? Individual termination of the start and finish leads from each coil of a humbucking pickup to a cable with four separate conductors plus a shield. This allows extremely versatile switching arrangments such as series/parallel, coil split, in/out of phase and so on.
What is the Bare Knuckle Four conductor colour code?
Black =start of screw coil
White = finish of screw coil
Red = start of slug coil
Green = finish of slug coil
For standard series operation solder the red to the pot tag, the black to ground (usually the back of the pot casing) and solder the green and white together.