Flickering or pulstating Headlights

Hey guys I didn't want to start a whole new thread since I'm having similar issues to here. My '70 Duster has flickering lights and voltage at all speeds, idle or above. I bypassed the ammeter and replaced the fusible link while I was at it but that was a few years ago; also installed Auto Meter gauges with a voltmeter. When the engine is running above idle the voltage will pulsate between about 14-15 and I can see my dash lights and headlights flickering with it. I'm thinking about trying the relay mod for the ignition switch but could it be something else? This issue wasn't noticeable the last time I was driving the car 2 years ago but since it has sat and I put another engine in this problem has popped up. I know the wiring from the alternator is still the old factory stuff could that be a source of the problem? Basically should I just try putting in new wire first or will that probably not fix the fluctuating voltage issue?