turn signal wiring problems

I have a 2001 century and I have problems with the brake lights, T/S, 4 ways, and tail lights. Only in the back. I think I need to replace the wiring harness. I have traced the problem forward with a test light.
I have a week light all the way up to where the harness is in a bundle near the front shock passenger side.
It hard to get too. It comes down from the fire wall from the main fuse box. Its all wrapped in the black plastic protective sheath. The light is real strong coming into the junction and comes out week. So I believe it's there I need to run a new wire harness. 4 wires back to the tail lights. Tired of paying mechanics money for a constant recurring problem. For now I have run a wire from the side T/S to supply the rear T/S, and tapped into the trailer light circuit for my rear tractor brakes. I am going to buy 30 ft of an outdoor grade wire designed for residential under ground use. It's very resistant to the elements.
I don't really understand how the brakes and T/S interrelate together. I thought they ran on the same circuit. The pig tail at the tail light has 3 wires. I believe 1 is tail light, T/S and the last one is ground.
Where and how do the brake lights come on. Anyone who can shed light (he he ) on this subject, your experience and opinion is welcome.
Thank you

 

I did for my brake lights.
Guess that's all I have to do.

 

That's the million dollar question.
I wanted it working right.
But I guess I'll have to settle for working.
Thanks for the reply.
Be safe

 

I un did all the splicing and installed new switch.
right brake light still not working.
4 ways work but not in unision. I will keep it the way it is and mess with it when I get time.
at least I know it's right. (Sort of) he he.