Brake pedal draws power stalls car

I have a 73 duster 318/auto(originally slant 6 auto). The other day I was driving and hit the brakes and it turned off the radio, all my gauges died, stalled car. I have an electronic ignition, if you 2 foot the car you can feel the power draw on the ignition and it causes a missfire and the car even over heats. The ammeter bottoms out as soon as I touch the brakes. What could be wrong? I had a similar issue last year but my tail lights weren't working and it turned out to be the light switch. Could it be the same problem again? My lights still work this time but same symptoms.