Re: Wiring help with PJ
DiMarzio's own series/parallel schematic diagram will work. My inclination would be to keep the Model J wiring conventional DiMarzio as far as the mode switch then reverse the destinations for the switch output and ground conductors.
If your P pickup has a metal screening plate, reversing its output conductors removes the screen from the ground side of the circuit, possibly turning it into an RF antenna. I suggest return the P pickup wiring to normal phase.