Need to verify the stator is good. (And for what it is worth, I have only ever changed one and the ignition side was bad, not charging side). The stator has 2 outputs. One goes to ignition, one to the charging system. You need to ohm the charging output (Yellow wires) Should have low resistance (like a few ohms) & not shorted to ground. I can look up exact numbers later if you need them. If ohms good, then the regulator is faulty (most likely).
OMC stators in general are much more reliable than Mercury. And very few regulators fail but that is where I'd put my guess.