Ignition on power in a 65 dart

I think that is what I would do too. But you'll need to fuse it well and make sure the connection through the dash is in great shape as this is the weak point of the Mopars. If you put to much load on that it could cause the point where it goes through the bulk head to get hot and burn up. That point is hot all the time by the way and you could use a relay in conjunction with a constant power to a switched power off the ignition switch.