looking 12 volt source in on and crank position

[Scawn]

I installed a 302 in my 1966 mustang. I need a 12 volt power source that gives my coil voltage in the on and also the crank position. I cant use any of the wires on the solenoid because they drop to 9 volts when the car is started. I cant use the terminal on the back of the ignition because it gives 12 volt power in the on position but drops out when you crank it.