When you take the idle volt readings, remember that a 1 wire alt. is self exciting and you have to rev it to approx. 1500 RPM to get it to start charging. Personally, I think 1 wire alternators are junk. A 3 wire (still has an internal regulator) has a remote voltage sensing wire and is far superior and I know several that have changed to one because of the problems you are having. Here's a great site that will explain it.
http://www.madelectrical.com/electri...hreewire.shtml
Jim