HEI Conversion for early A-Bodies

I've been trying to convert my 1964 dodge dart 270 to have an HEI distributor and I've run into an issue where I can't find a 12-volt wire to run the distributor wire to that only has 12 volts while it's starting and running they all seem to want to be at 12 volts all the time or drop down to 6 and all kinds of stuff. I was wondering if anyone had an idea what wires would work because I just have a wire going straight to the battery and I have to connect it and disconnect it when I want to drive it.

so any help/wiring diagrams would be appreciated!