Lighting problem

With the brake light problem. I have 12.6 volts to the hot side brake light switch, 12.6v on both sides of the switch when the pedal is depressed, and 12.4v at the plug on the white wire at the steering column (the brake light wire feed). If I plug in either of the 2 used blinker/4 way switches I have 12.6 volts on the hot side of the brake light switch. Then when I depress the brake pedal, im down to 11.4v on the hot side of the brake light switch, and 0 volts on the other side of the switch which leads to 0v at the plug for the blinker/4 way switch. Any idea of what is going on here?