My 70 cuda starts up then shuts down soon as I release the key. I was told to check the ballast resister with the key on with a test light.. I do not have any power on each side .
You found the problem. Test this by bypassing the Ballast Resistor with a small jumper wire, and start the car to verify its bad. Once confirmed, replace the bad Ballast Resistor.
Mopars of this era used Start 1 & Start 2 power wires to the ignition. The car runs on less than 12volts by passing it through the Ballast Resistor to extend the life of the coil = Start 1 ( key in the on position). It uses a full 12 volts to increase the ignition output during the cranking phase of starting the motor = Start 2 (key in the cranking position.)
The two ignition power sources, namely Start 1 & Start 2 are mutually exclusive. That means only one of them is on at a time due to the design of the ignition switch (the key switch).
The switch between the two power sources is very fast as the key is released from the cranking position to the run position. That split second switch is enough to cause EFI conversion set-ups to have problems with starting and running, but not enough to cause problems with regular points or electronic ignitions.
