Hi guys/gals. I have a Duncan Custom that I am putting in my Dean Caddy and I have a question regarding the wiring. I stripped the casing off to reveal the 4 wires inside but there is a plain silver wire as well that does not have a casing around it, what is this wire for? Black is hot, Green is ground and red and white are optional depending on configuration but there is no mention of this plain wire in the diagram, anyone have any ideas? Thanks.