I'm not sure if I am reading your schematic correctly, but here is some more details. The pull switch is on the tone pot so finding parts may be even easier. When the switch is pushed down the setup works just like a standard harness, panning from one humbucking pickup to the other. With the switch pulled up and the panpot is in the middle position the two pickups are just like the former setting, both humbucking with all four coils of the two pickups in use. As the panpot is turned clockwise the signal moves gradually from the 4 coils to just the 2 outer coils; when the panpot is rotated counterclockwise the signal gradually moves to just the 2 inner coils. It really is a great way to provide a variety of tone with a passive system.