battery overcharging

I have an 85 GT. I am having a problem with the battery over charging and boiling all the acid out of the battery. I have replaced the external regulator, the alternator and have had several new battery's but I continue to have the same problem. The last time that the auto parts store checked the system they said that it was definately my regulator so I replaced it and put another new battery in and still having the same problem. Any help is greatly appreaciated.

Id say the regulator you put on is broke thats the only thing that can overcharge a battery what does your voltage gauge do does it jump around or go over 15??