Weird wiring behind taillight?

Hey all!

I recently migrated from the 1st gen to 2nd gen world, and naturally have begun tinkering with the new truck. So, I'm beginning to notice the past owner did a few weird things with wiring, and I'm hoping y'all can help...

Last weekend I picked up new to me shell for the bed, and I went to start wiring the 3rd brake light/dome light when I discovered that this truck must've had a shell previously. There were 3 wires behind the taillight that have been chopped and just taped. Awesome right?! Not so much... It turns out that I can't find 12v on any of these wired in any combination. (Brake depressed, ignition on/off, etc.) So after looking further I find some weirdness with said wires.
2 of them are in a loom together, and run down along the frame, into the cabin grommet below the driver seat, and then tap into a circuit right there under the door sill. WTF?! And the other just runs to what looks to be like the trailer circuit but I'm not 100% here. Than it is completely smashed between the frame rail (grounded maybe?) Check out the pics below, I'm hoping maybe someone has seen this before.

 

I would just pull all that crap wiring out and toss it. Use liquid electric tape where the wire taps were used.

 

Yes I agree. God knows what was jerry rigged. Great way to cause a fire or screw something more serious up.

 

This is basically the conclusion I have come to at this point as well....

But why would someone take the time to run all the way to inside the cab? It's always interesting what you find when you start tearing these trucks apart.

On that note, does anyone have a recommendation for tapping a 12v source for the shell dome light? Something near the back? I'm guessing this may have been what the PO was going for, but I cant pick up any power whatsoever from these lines..

 

My canopy rear glass lock taps into the truck there. It un/locks with the truck doors via the key remote.

 

I don't think there are any lines back there that are hot all the time.

 

The blue/red and blue/black are your lock motor wires. So it’s probably for a locking tailgate actuator or for a cap with a actuated lock.

 

Yeah, that's what I'm afraid of.. Guess I could just repurpose these lines that are run into the cab already and find a hot 12v source. it looks like good quality wiring with high heat loom, so why not.

Ok now we are talking!! Thought it might be something like that - but I didn't have a schematic, or anyone around to hit the lock button while I looked for the voltage spike on the taillight end.
I didn't even know there where auto locks for truck toppers, That's Faaaaancy. Picked my topper up for $300 on FB Marketplace and have to replace the old salt-laden locking handles.. Gotta love Utah/Idaho winters, haha.

 

That's fancy, I had no idea this was even an option! Sounds like mystery solved..

 

Doesn’t pop a lock tailgate lock have the wires connect under the drivers side sill cover? I don’t have a pop a lock but I thought I read that’s where the connections for it are made.

 

I have some auxiliary lighting on the back of my truck - and ultimately I just wired it to the trailer harness (with weather proof taps). It was convenient to do that at the time. But..... if I wanted to make it remotely switched, hiding the rear end wiring behind the driver side tail light would be a convenience. Easy to use the tail light as a pop out wiring cover without groveling on the pavement or muddy ground. There are times when the aux back-up lights would be a help during trailer hook-ups, camping or loading. A switch in the cab, rear end relay off the trailer power and it would be available without the truck being in reverse.