[patrickt]

I see you ran an extra ground to the voltage regulator, which is good, and poor grounding is the #1 cause for a varying voltage which would make for a varying current which would cause your ammeter needle to waver. Just to be absolutely sure though, get a nice four foot long wire with alligator clips on both ends and put one on your voltage regulator case and the other on the negative post of your battery, then see if the wavering is still there. If so, confirm that your voltage at idle is really bouncing around and up in to the 15 volt range, which it shouldn't. Generally when that occurs it's because of poor grounding at the voltage regulator and I'm still suspicious of that.