I think, as was stated previously, I think a bad connection is the issue. I would, as suggested use a multimeter on the voltage setting, and look for a voltage drop, especially to ground. You might even try grounding both the alternator and the regulator together, to the same ground. If this eliminates the problem, a ground is the issue. The plastic smell could be that the current necessary to charge the battery going through the ammeter is heating the connections. This might be the result of normal operation and the current necessary to charge a partially discharged battery is more than the factory connections can handle, especially with the time involved to recharge it. You might try a battery tender or trickle charger on the battery. This would keep the battery fully charged, and allow further testong of the "issue" as well. Let me know...