Tail light/brake light harness plug in.

[CURSED GEARS]

Greetings.
Been rebuilding my truck for the last few years and have been working on the wiring harnesses.
I've used the search function and read a lot of threads pertaining to the tail light wiring harness, but no specific info on what I need.
Here is my question. The plug in to the wiring harness on the inside of the cab, that runs through the firewall, what's it look like? I assume it matches up to the intermediate wire that runs down the channel of the frame. Does the inside connector, (plug) attach to the main inside harness under the dash?
I took this harness out a couple of years ago and can't remember. I have been working on my harness cleaning it up, repairing wires, and such, but can't find the inside plug that goes in the firewall any where. I seem to remember a smaller wiring harness detaching from the main harness when I was taking it out of the cab and wonder if that could be it?
Anyway. If you guys let me know or a picture would be helpful, I would appreciate it.

Cursed Gears