1984 Dodge Aries charging system problem

I have a 84 dodge aries with a 2.2 liter and can not get the alternator to charge. I replaced the alternator and voltage regulater after the alt went bad it worked a week and quit I replaced it with another alt but was given a bad one with a short that caused part of the harness by the battery to burn up. I repaired all the burnt wires and replaced the alt with a 3rd known good one now my problem is that I have checked for continnuity from the alt to regulater ground circuit checked alt output and field wires for power checked for shorts or battery drains and everything has checked out fine I get 12.6 v at alt output wire and 12.6 v at both field wires but when the car is running I watch the voltage steadily drop from 12.6 down to 11.5. The only time I see a charge is if I full field the alt by shorting one of the fields to ground and I get a 15+ volt charge as read at the battery terminals by a volt meter it appears to me that the regulator circuit is not functioning properly but I am getting power to both alt fields and both terminals at the regulator. Im stumped any suggestions would be appreciated as I havent seen a k car in about 10 years up until now the only things im leaning toward now are the starter solenoid or the computer but have no idea if those would help and I dont want to keep replacing parts as the car belongs to an elderly friend who doesnt have much money and has already paid a shop over $400 to look at it and they just cut a bunch of wires up and then shrugged their shoulders and told him they dont know.