Alt replacement

Your 68 wiring harness has a single blue wire from the ignition switch that goes to the engine bay and feed 12 volts to ignition system and charging system. much like the headlight wiring, it was barely adequate for the OEM equipment. Simple solution is to add a relay here also. Blue wire signals the relay, 12 power on sufficient ga. wire comes from battery ( stud at starter relay ). Equipment gets the full 12 volts it needs, under dash wiring and switches live longer.