1998 E430 Charging issue
 

Hello all!! I have a E430 thats not charging properly. I believe the cause to be not enough voltage on the small wire leading to the alternator. If you rev the car up it charges fine but as soon as the rpm drops below 2000 it stops charging. Ive already replaced the alternator twice and it still does the same thing. I checked a 1997 E420 and it has 12 volts on the small wire. The E430 only has 6 volts. Does anyone know whats responsible for the voltage on that wire. Im thinking maybe the ignition switch but I dont have a wiring diagram to troubleshoot from. If anyone has any ideas I am all ears. Thanks for the help in advance.

If you remove the small blue wire at the alternator (circuit 61),
and measure the voltage with the key on engine off, 12V.

That signal comes from cluster.