So I found that just dangling underneath the truck. Followed the wire up and pulled it up. It has another wire coming off it and then going to a ground connection - see pic below.
I then put 2 and 2 together and it seemed whoever replaced the negative battery cable - used the wrong one. As the one that was just dangling had 2 smaller wires coming off it that seemed to go to a sensor right behind the battery - since the one they got didn't have 2 smaller wires coming from it, they made this shitty splice. One wire from the negative battery connection and 2 larger wires that lead to the electrical connection (I fixed the shitty splice today - that is not my handy work below). See pic below.
I then followed the random battery cable down and found it goes to this sensor. Is that my shift solenoid? So that random battery cable wire is grounded - but getting power from where? I know I read that the shift solenoid is in the oil pan. Could that be the reason for my check engine code 54? The large white thing in the pic below is the oil filter. See pic below.
Sometimes when I put the truck into gear (auto) it won't shift into the gear. So I'll give it steady gas (which raises the battery voltage needle) and it'll shift (not a clunk shift) into the gear I put it in. The voltage on my battery while off is 13. While running it bounces between 12 and 13. When the idle goes up (after the check engine codes are done flashing) the voltage goes up to 14 or 15. Then it drops back down to a 600rpm very rough idle and the check engine light comes back on.
I'll be replacing the battery tomorrow.
Code 54 is signal high IAT or VAT sensor...malfunctioning shift solenoid. I've since replaced the IAT sensor with no change in codes. The IAT sensor gets 13v and should only recieve 5v. I don't really want to run a test wire because of the current wiring issue. And the check engine light will very randomly - go off at any given time and the truck will drive at the normal idle and be able to shift into OD at 55mph. As long as the check engine light is on, the truck will drive with high RPMs around 3k and higher and never shift into OD.
anyone with a microfiche or wiring diagram?