I have a 1984 dodge d150 prospector 2 wheel drive pick up . Slant 6. My problem is my headlights go dim at idle and my heater fan drops down in speed. I have replaced the alternator and voltage regulator also the battery. Had auto zone do a check and they said the alternator was only putting out 46 amps. Thought about taking it off and having it check to see if it was faulty to eliminate the alternator. A friend of mine told me he had a dodge that done the same thing to him and it was the volt gauge. I looked online and there is a voltage regulator for the gauge cluster. My question is would the gauges cause a draw down affecting my lights and battery charge? Any idea's would really help

See if this link helps:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563-10.html#post1973613

Set the idle rpm to specs. The gauges won't account for the dimming lights and battery charge.