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My dad has a 2010 GL450 4.6L, recently when he was driving the charging system failed. I removed the alternator and the main battery and had them tested twice at AutoZone (2 different stores) and they both passed. I checked grounds and power for the alternator and I am getting battery voltage. When the cars on it will not charge at all, it stated charging once and when I put it into drive it stopped charging. The reference wire or exciter wire (the 1 wire) when grounded with a test light showed 3.8v while the car was running. Does this seem like a exciter problem? I'm not sure what it is suppose to be as most cars it's pretty close to 12v... Vehicle on Vehicle off Exciter wire grounded 3.8v (car on)