420SEL Electrical Mystery

This is an 86 420SEL with the following mysterious electrical symptoms. Sometimes stepping on the brake pedal kills the running engine. I just experienced today that flipping the turn signals also stops the car. It seems like the above actions would "sometimes" shut off power to many circuits (Most gauges are off except SRS. But still have power to other equipments such as window and lights.) More over, once the engine stops, the ignition switch remains in this limbo state with no power to some gauges. So the car won't start. However, I found a way to restart the car by touching the brake pedal again thus enabling the ignition switch.(Not consistently on every try though!) Leaving the car alone overnight "seems" to re-enable the ignition switch as well. But the problem starts over again. I greatly appreciate any suggestions for solving this mystery.