So I was working for 12+ hours two days ago and got to my truck about midnight, and when I went to turn it over, the interior lights work and so did the instrument panel, but when I tried to turn it over, it clicked for maybe a half a second and simultaneously turned off and lost all power entirely. I went back the following morning around 10am and it started up and ran perfect. The battery and alternator both tested perfectly fine also. What could be wrong?

 

You had corrosion / oxidation somewhere in the battery cables (battery post, battery end cables, loose wire at the block for the ground wire, loose wire on the positive cable, etc.)

RwP

 

One of the battery terminal connectors is pretty corroded, so much so that you can't loosen / tighten it anymore, it just sits the way it is now. I appreciate the help !

 

Well, there's your problem then! *grins*

A new terminal, or even better, a replacement cable is indicated.

RwP

 

For a temporary, emergency fix, just put a sheet metal screw in between the battery post and the cable connector.