I have no interior lights, windows, A/C , heater, backup lights, day/night light sensor, or locks. It also won't shift itself! And I am getting no codes. Replaced a relay switch but no effect. Any ideas???

 

Computer? Had that happen on a 1980 Thunderbird I had. ( I know Ford vs Chevy) I was going down the road when everything just cut off. Tow it back to a dealer ship and it was the computer..it happen several more times after that. (Ford had a serious problem back then with the computers) Finally my (EX) 1st wife totaled the car out and fix that problem...Her boy friend was driving...She got the car in the divorce.
Anyhow you might want to give that a go.

 

Maybe you burned through a fused link, If remember right there are two wires that run from the alt post, one goes to the bat, and the other goes to a distro block. Possibly you fried the wire to the distro block. Just a guess.

Or... Its a bad ground.