Generator Overchargeing

[modelamodela]

The generator was working fine, but stopped charging, so it was replaced with another that worked OK.
Another Model A I have developed charging issues, so I pulled this one off the shelf and put it in, and now it does appear to be charging really high, sometimes it is at about 8 amps but as soon as the car is going 20+ MPH the rate is pegged at 20 amps. Moving the third brush does not change the charging rate.