Hardipk5

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)

Max Blast

You need to run an alternator load test in xentry, the mb specific scan tool to really test these.

typically it’s just the voltage regulator that fails on the OEM alternators. Replace that and you should be back up in the 13.5s.

Sallad

What voltages do you get while the vehicle is running? Check at the battery posts (jumper posts under hood is good enough)

Car off should be around 12 or so volts
Cranking, shouldn't go below 10 V
Running should be around 14.5 V

Your exciter wire seems low.