Alternator ailments

[Kneale Brownson]

Finally got a chance to test my charging system that started acting up while we were in Columbus, OH, over the weekend but managed to get us home.  
   
  With the engine off, the battery reads 12.5 volts.  Same reading for the positive terminal post under the hood.
   
  With the engine running at idle (voltmeter in car reading ~12), the reading with my multimeter is 12.17 at both the battery and the jump post.  I presume that means the regulator ain't regulating properly, but the dreaded wiring "weld" in the passenger footwell is passing on its voltage without any resistance.
   
  Is it possible the "exciter" circuit (blue wire) would be the culprit?