ok Stoo, not thru the switch, the wires are routed the same, use common plugs along the frame, go to the switch/turn harness for power - the brake light wire [1 to control both sides] comes outta the harness to go thru the brake switch - on a TF55 the tail wire is black, the brake wire white
and Billybolt, the harnesses are wrapped originally, as are the repros, and it's best that they are - if the truck has a [not too mutilated] original harness the color coding is the easy way to track wires, and the reason they're color coded
Bill