One day going out to my truck, trying to start it, nothing, no clicks or attempts to turnover. Tested the battery, was fine. Replaced the starter, nothing. Replaced the battery cables, were kinda bad, nothing. Buddy told me about fusible links, replaced the ones the solenoid wire that runs to the altenator then to the firewall, still nothing. I don't know what to do, any help would be amazing.

Looking around the engine, found this wire, coiled up on the valve cover, I don't know if it got torn off or what, but was just sitting there, has enough slack to get to the solenoid, but there's no wire loom for it. it does run along the firewall up and over then under the brake drum through the firewall, no idea what this wire is for.