There's loads of wire diagrams etc here:
https://www.bareknucklepickups.co.uk/supportIncludeing, under FAQ, this:
WHAT IS THE BARE KNUCKLE "FOUR CONDUCTOR COLOUR CODE"?
The colour code we use goes like this: Black: Start of screw coil; White: End of screw coil; Red: Start of slug coil; Green: End 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.