It looks like there is a fourth wire coming out of the Duncan wiring diagram

[357mag]

The 3-way toggle switch I ordered has 3 wires coming from it. One goes to the neck volume, one goes to the bridge volume, and the third goes to the output jack tip. But when I look at my Duncan diagram which I printed it appears there is a fourth wire coming out of the top of the toggle switch and it looks like it goes to the back of the bridge volume pot. Can someone tell me what this wire is for? Is it just an additional ground wire that needs to be there? This is the toggle switch assembly I ordered:

https://www.ebay.com/itm/16249537399...53.m2749.l2649

[357mag]

I think when you look at the toggle switch assembly I bought you can see a ground wire already connected to the braided wires. I think therefore that is the ground wire already grounding everything.

[Pontiac Jack]

2 x input. 1 x output. 1 x ground