Hello.

The only 12v source for both start and run on your car that isn't constant power is the positive side of the ignition coil, and the wire going to it from the firewall connector, and that's only about 9V in the run position. The 64 1/2-66 cars don't have anything on the fuse box that has anything to do with the ignition circuits. A lot would depend on what you are trying to accomplish here. If you want to hook up an electric choke that would be one thing, but, if you are trying to hook up an electric fuel pump, that would be another thing entirely.
