Art,

My alternator ground wire that attaches to the outboard end of the alternator broke at the connector.  I think the main inlet wind blast made the wire move just enough to cause it.  The symptom was intermittent charging on the main alternator. 

Steve Colwell  Legacy IO-550

 It only trips when operating on the single battery.  It is a two battery system and has operated on a single battery for years with no problem.