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Hi eveyone. Have a 2008 cayenne 957 4.8 S. Vehicle has been sitting parked for almost a month.A couple of weeks ago went to start the car and it barely turned the starter. Pulled battery which is less than a year old and charged it. Put battery back and cat started fine but voltage started to jump and fluctuate from 14 to 12-11.5 8
on the dash. Played around for a couple of days and voltage was jumping and battery seemed to drain. Finally voltage went to 11 12 and never up to 14v. Figured alternator went kaput and bought a used one. Installed and same thing. Bought a set 4drrebuilt tested alternator and still the same problem - no charge from alternator to battery. Im pulling my hair off what can it be. Open carpet by the left driver foot and checked wires and all is good . Please any help will be truely appreciated. Thank you in advance

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First of all get the Crank Current (CC) of your battery checked because voltage doesn't mean much, you need to know the health of the battery.

Check MB23 as you have already checked GP25? Check the fuses.

 

The alternator must have windings excited to make power so it could be on the regulator side of the system with a problem with low voltage, Bad ground?

Here is the Charging Circuit.

 

Charging Circuit.png

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