Wiring for the brake lights in the diagram makes no sense at all. One of either the blue (likely) or the black wires on the tail light is the hot side of the brake light and the other is for the common (ground). Run a wire from the red hot to the in on both of the brake switches, then from the out side of the switches together to go to power to the brake light. That way if the switch is actuated it sends the power to the brake light.
Horn switch I suggest the easiest way would be to locate the switch how you want it and then remove the paint so it can be in good electrical contact with the bar.