Yes a wiring diagram would be nice. or even the type of guitar and the setup you put in it.
It is common to see the ground from the pots with a wire going to the pot body. So too, i have seen a wire going to the inside of the bridge (where the springs are on the electric guitar).
Also when you flick the switch to the "off" position you may be switching off the grounding for the switch, and most possibly the grounding for the guitar. So find out what type of toggle switch it is, aka DPDT (Double Poll Double Throw) or SPST (single pole single throw) etc. Then ground one of the pins that are "closed" when you turn the switch to the off position.

Merls