Having the same issue. The battery and hot wire to the voltage regulator are connected under the "D" side or under the "C" side?
Check this diagram:
http://www.hunt101.com/data/500/D-R_Regulator_001.jpgThere should be only one wire to the battery side of the ammeter. Every other connection including the battery wire from the regulator needs to connect to the "load" side of the ammeter for it to function properly. The simplest way to figure out ammeter polarity is to connect the wire from the battery or the starter cable to one side, connect all the other hot leads to the other terminal and turn on a bunch of accessories. If the ammeter needle swings to the "discharge" side, you're connected properly. If it moves toward "charge" with the engine off and current flowing, swap the leads side to side.
Jerry