My dad has a 1991 dodge dakota with a 5.2L that will not charge the battery. we have replaced the alternator and battery but while thetruck is running the voltage will stay constant until you give it gas and then the battery totally drains. I've checked the cable from the battery to the starter and from the battery to the alternator, all ok with a meter. I also checked all grounds and even added another to see if i was crazy. Any Idea???