My amp gauge needle keeps bouncing. Is it the gauge, altenator, or voltage regulator?
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It's the alternator. One of the doides have gone bad causing the needle to go in the opposite direction. Instead of having DC current you are getting AC current. Be careful if you have a MSD box or any other type of ignition box the AC current will zap the box .
A stock Pantera charging circuit sends 100% of the alternator output thru the amp gauge.So if the alt is begijning to go, or the battery is low causing a very high drain when starting, you'll get radical swings of the gauge needle. After fixing whatever hardware problem you may have, I suggest either adding a simple 'shunt' or current bypass to the gauge, or purchase a reworked stock gauge from one of the vendors. A shunt bypasses some or most of the current around the gauge in a parallel circuit, decreasing the violence of the needle swings. As the amp gaige is not accurate anyway, we tend to use the needle as a "plus-or-minus" charging indicator and the loss of needle travel doesn't bother us. Stock gauges have caused in-the-console electrical fires from loose connections, too.