M931A2 Running Lights.. Need Help

[JohnnyBM931A2]

I posted a thread a while ago regarding my rear running lights not working. Every single other light works on the truck, with the exception of those 2 bulbs. As was suggested, I started trying to check the connections. I pulled the plate off behind the rear light on the passenger side, turned on all the lights on the truck, and then pulled the 4 connections apart one by one. Using the test light, I was only getting power to one of the wires (the one that feeds the bulb for the turn signal and the brake light, which is the same bulb.) So... Yeah. I'm guessing 1 wire is for the running light that I have an issue with, and the other 2 are for the blackout lights?

I'm not sure where to go from here.. I opened up the wiring harness (about 30 layers of electrical tape and several coats of paint) up above the pintle hook. I saw a big bulge in 2 places, so I figured there were connectors in there. Well.. after I cut those 2 spots open I saw what almost looked like rubber fuel line covering the wires. It is solid, and it looks like the ends are sealed. Does anyone know what that's about? Is it some kind of hardcore shrink tube?

Does anyone know where the other connections are in the circuit that I am trying to diagnose? I did see a NOS rear wiring harness for sale on eBay, but I am hoping to avoid that if possible. Though it would certainly be nice to have some new wires on at least part of the truck. Most auctions don't specify A1 or A2 with the harnesses.. Does it matter for the rear one? And does anyone know the actual part number for the rear harness that I might need?

Thank you guys.. This is a "simple" problem, not like a blown engine or something, but it still keeps me from driving the truck just the same

 

[JohnnyBM931A2]

For what it's worth, the inside of both taillights look brand new.. Still have the grease on the bulbs and everything. And all 4 of the taillight connections that I pulled apart looked ok.. No noticeable corrosion. I kind of wonder if they were replaced in a failed attempt to fix this issue..