I want to add a phase reversal switch to my 5120 to put two P90s out of phase with each other. I saw on this site a diagram for the switch, but I'm not sure where to solder the grounds and leads. What gets soldered to the + & - inputs and outputs of the switch and how does this all fit into the wiring harness. What arrangements must be made to make this work? The pickups have a single lead and a braided ground wire.