brake lights not working please help

I know this is a very common problem with these GMC trucks but this driving me crazy now, i just bought this 96 gmc yukon never thought about checking all the lights working before purchasing until i got pulled over for no brake lights no running light well to keep it short the taillight wiring under the truck is a mess! the previous owner installed one of those LED strips that go on your bumper and messed the wiring all up BAD so i pulled the whole wiring harness out and ordered a new one. Now i have running lights, both turn signals, reverse lights hazards and JUST THE TOP BRAKE light no lower brakes lights. If i run power manually to the lights they work so i know my mother boards are good, checked all the fuses , they look fine what has me really confused is that it doesnt have a brake light relay? there is a location for it but it has no power/wiring to the slots? the cover also states it should have a big fuse for the STOP/ HAZ lights and its the same thing no fuse there and nothing running to the slots? after some research i decided to change the brake switch just because it was a cheaper option still the problem well then i changed the multi function switch still the same problem i did notice that the switch has a small 2 wire harness that i have no where to install it on? Any help is GREATLY appreciated as im going crazy trying to fix this!