I'm not 100% sure but I think the whole wire from the firewall junction block to the coil is a resistance wire.
You can check by taking a voltage test at the terminal block on the interior side, it should be 12 volts.
You can replace the wire , it's in the terminal marked K on the junction block. Or cut the wire near the junction block and splice in a new wire. I THINK the resistance wire has a certain amount of ohms of resistance per inch or foot if you left a small amount of the resistance wire and spliced in normal wire you may get close to 12 volts. Better to take the junction block apart and replace the wire though.
I mounted a relay on the firewall near the HEI controlled [turned off and on] by the by the original wire and powered with full alternator voltage [14 volts] from insulated terminal block also mounted on the firewall. If you want a clean original look change the wire.