There are two separate wires that power the coil.
One has power only during cranking and bypasses the ballast.
The other only has power when the key is in the run position and goes through the ballast so the coil runs at a lower voltage so it doesn't overheat.
These two wires are the ones that need to be tied together for aftermarket ignition system like HEI so the ignition system gets 12v in both positions of the key. (start and run)