How to run a wire from inside of a cab out to the back???

If you want to be OCD about it, run it through a grommet in the firewall and squeeze it into a split loom that goes to your pigtail socket.

 

Wireless cams could be an easier way to do this, they only require a 12-24V feed, sends to a dash display.
Here is one I found on amazon, waterproof cam

https://www.amazon.com/Digital-Wireless-Waterproof-Transmission-Distance/dp/B07DNBJBQQ

 

Drill a hole

 

Open the hood and look for the wires going into the cab. Every hole is protected by a rubber grommet.

 

You're missing the point. You go through the firewall and then under the cab. That's how the factory gets power from the fuse block to the switch and then on to your rear lights. If you look under the truck, you'll see every wire under there begins at the firewall, one way or another.

 

no it don't I use wireless and they work very well.