My '40 Ford has a 350 Chevy. I'm using a new Tuff-Stuff 100 amp 1-wire alternator. At idle, the voltmeter reads 13.9 volts. When the rpm is raised, the voltage starts dropping to around 12 volts. I had the alternator tested and was told it was putting out fine. The guy told me that 1-wire alternators don't always read voltage the way regular alternators do. Anyone have thoughts on this?