Purney,
Any wire attached to that nut on the starter switch will have power all the time...not switched! The large cable from the battery proper is obviously the conduit to supply power TO the starter to make it spin.
The other large wire, 10 gauge or so, is the supply for all electrical items on the truck AND the path the power takes back to the battery from the charging system. This bolt is sort of the master connection for all things big and powerful.
I don't think there is a third wire normally attached to this point. It doesn't mean there can't be though. The wire to the positive (+) side of the coil MUST be switched. No wire running from that bolt on the starter is switched. They do make a starter switch that has a small bypass terminal on the side that is involved with the ignition system, but it isn't a big bruiser, and your rig isn't configured to use it.
Stuart
