As dd said the "start" wire only should have power when the key is in the "start" position and when the engine starts and you return the key to the "on" position you should have power to the "in" terminal of the ballast resistor, it sounds like you only have ignition power when the key is in the "start" position so remove the distributor cap and turn the key to "on" and check for power to the points if there is none then you have a faulty ignition wire or a faulty ignition switch, did this problem start happening all of a sudden or is it after a rebuild