Ignition on power in a 65 dart

Your car already has the convertible top on there on one of the studs.
But yea.
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You got to decide whether you want the loads on all the time or only with the key.
And it depends on the loads.
The RUN circuit was for only for critical items to run the car - ignition and field. It had no fuse (other than whats inside the mechical VR.)
Everything else that needs the key on is on the 'accessory' feed.
You can piggyback onto either acc'y or acc'y switched at the fusebox. But of course that might overload the feed wire if your new items are run at the same time as other stuff.

Keep in mind that IF you drain the battery, when the car is restarted, the charging rate will be high. That too can and will slowly damage wires and connectors. If its too high it may also damage the alternator and battery.