wiring brakes

[CG]

i bought a trailer from a friend. it has electric trailer brakes. he wired it up himself and discovered when he turned on the blinker the brakes went on and off. so to fix this he cut the wires. my 72 burb has one of those trailer brake things you see mounted under the dash. personally i have no idea how they work. it has a brake line that goes to master cyl. and then it has three wires. as you can see in the pic its only using two of the wires and those two are spliced into an orange and blue wire. the orange one is part of a ribbon wire, one orange one black. when it comes out from under the dash and through the firewall the orange goes to trailer harness. the black wire (the one in the ribbon with the orange) starts on engine side of firewall and is spliced with a fused red wire and the red meets the blue (that came from under the dash) on the other side of the fused link. from there it is one blue wire that goes to batt hot and the other end is on the trailer connector. whew, you following me? ok now my questions. why is that one wire not used? next one, each of my trailers 4 backing plates on the drums has two wires coming out of them. how do i wire them in? one side to the orange and one side to the black wires we were talking about? im going to go pick up my purchase from cheyenne10 and i want this thing to be working perfectly. i already have the rest of the wiring figured out. this brake thing is messing with my head...thanks for any help guys.

oops should have posted this in general...sorry