For you to understand what the problem may be, you must first understand what is going on in the alternator.
For the alternator to work it needs to be "energized", for that to happen it needs to have an excitement wire. For the one wire pieces of crap, they need to have an internal connection to the field of the regulator, this is literally done with a small conductor from the battery lead to the regulator. So it wont happen with those, the battery will just simply run down until it is dead.
If the battery lead is not hooked up to a 12V source and the field is left "wild" to the ignition,there is no voltage regulation and some really cool stuff starts to happen.
The regular old Delco Remy alternator can make as much as 300 volts if left "free", this is not DC voltage, but rather AC. This can blow out the diode trio and potentially blow up a battery if left unchecked.
When I had the shop, the first thing we would do to a customers boat when they had an electrical problem was to disconnect the alternator and run the engine on a dyno. The charging system was then checked out, many times it is either a ground issue, a bad diode trio or a failed regulator, I have seen very few brushes wear out and only one failed stator in over 15 years.
EDIT;, I guess I owe an explanation of why I dislike the single wire kits.
The one wire alternators cannot take into account the voltage drop generated by most boats electrical systems, the way they should be wired is so the field or "reference" voltage should come from the dash panel, this ensures the alternator generates enough juice to offset the drops from the long wire runs and questionable electrical terminals.
I am also not a fan of the ammeters found in many older boats... Ditch them for a quality voltmeter IMHO.
GT
