The coil has a key switched hot wire in it that is hot during cranking and in the run position, this is the + wire for your ignition system. Look up a basic contact point ignition system diagram, as well as a basic electronic ignition system diagram for clarity.
Also, the ignition key switch in the Amazon’s is 50+ years old now, a universal key switch is probably more robust and reliable at this point, and the key won’t break in the barrel. Personally I didn’t even cut my armoured cable, I pulled the key switch from the hole and tucked it behind the dash, then transferred all the wires required to my universal key switch. I guess in the future some purist could set up my system to be stock again, but it would not run as well as it does now.