I finally figured out why my voltage had been creeping up - I was losing a small bit of voltage with each crimp and connection and section of wire in the alternator field circuit (went from the main buss, through a fuse, 4' to a switch, then 4' back to the alternator. That added up to 0.4 volts over the length of the circuit when the field was drawing 3.5 amps. If that draw ever goes up in flight the voltage drop would be higher. More importantly there was a bad crimp in the b-field wire which would have been causing an obvious drop in voltage between the alternator output and the rest of the electrical system.
I fixed the crimp and installed a relay near the alternator to handle the field voltage. This not only got my operating voltage back down to 13.8 volts, but also removed the last bit of alternator noise from the headsets. Cool!
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