The three wires are signal, 5v and ground. Use a meter to find out which is which. If you can't do that, red is always 5v, black is always ground. If they're red yellow and blue, yellow is ground.
You simply connect your two brake wires to the signal and ground wires, leaving the 5v (red) disconnected. It doesn't matter which way round your brake wires go because it's only a switch .
