Bill,

Jim has it right and rather than add to or confuse the issue I suggest you and he communicate via some simple wiring diagrams. I think you are not yet clear on how simple this is. All you are doing is using the signal circuit (whatever you pick, such as a brake light wire) to energize a coil that closes electric contacts to close the 12V brake controller circuit. Four wires. 2 to the relay coil (one of which is a ground wire), one 12V in from your 12V power source, and one 12V out to the brake controller.