I have a 93 isuzu npr with a 4bd2 engine. The battery light and vaccum light is on. Put a voltmeter on and its not charging (12.0-12.5). I have put a test light on the charging fuse while running and no power. I have changed the charging relay and still the same thing. I have also pulled the the 3 prong plug from the back of the alternator and have power on one when i turn the key on and one when the truck is running. the other has nothing. I have also ran a new battery wire from the back of the alternator to the battery. Any suggestions would be appreciated before i have to make the dreaded trip to the dealer.