On Going no start

Just a bit of the story, 69 Cuda, 318 auto, have installed Pertronix dist and the correct coil, have been tracking down issue of no start. Last item on list was to replace the coil to dist. cap spark plug wire [ did replace the whole set of plug wires, but coil wire need to be longer due to where I have the coil mounted], and unhooked the electric choke wire I had hood to the coil. The other day I was able to try to start the car again, it seemed like it wanted to fire while in the crank key position, but as some as you left the key god to run , it did not want to try to fire any longer [ TO NOTE THERE IS NO RESISTER BLOCK] so I think I have lost the run power going to the coil from the ignition switch, I think I need to install a relay to keep power [ 12 volts] going to the coil so the car will start. Since I do not have power that will stay on from the ignition switch , in the run position , where under the hood should I pick up 12 volt switched power source for the relay trip power?