1971 Dart: What causes overcharging?

My factory Alt meter is almost pegged at cruise. What is the cause? Thanks.

bad voltage regulator

As Brad said likely the reg. 2 field terminal alt/flat 70 up style reg I am assuming. The batt is fully charged & this just happened out of the blue without a batt change? What I'm saying is you are not using the car to charge up a run down battery correct? Un plug the triangle reg terminal till you solve this as this "full fielded" condition is extremely damaging to the batt/terminals/bulkhead/any lights or accessories on as they ain't designed for 15+ volts even for brief periods of time and haveing the batt deep cycle a bit from being run down some ain't the best for a batt but is the lesser of 2 evils (by far). With reg connector plugged back for a moment in I would unplug the green field wire from the alt for a quick test & if it stops charging then I'd likely get a new flat reg.

Simply a bad ground at the voltage regulator could also cause this. Unbolt the regulator, clean up a few spots so there is bare metal showing. Hit with some grease, re-attach regulator and see if it still does it.

If it does, then yes, bad reg.

Thanks. I will try all those things you posted tomorrow. Thank you.

If the green wire is grounded (pinched in the valve cover for example) then you will get full field action out of the alternator.

Go to Autozone and get a solid state regulator. They are around $20 and work great.

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Go to Autozone and get a solid state regulator. They are around $20 and work great.

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All dual field terminal alternators use solid state regulators, stock.