I have just bought an 07 l322 3.6 tdv8. the previous owner has had some charging and battery problems. The car suddenly just died and was towed to the mechanic. New battery(AGM) installed but not charging, leading to a new alternator being fitted. The new alternator he had installed is ofcourse an unoriginal ATL Autotechnik branded one. The car is now charging at 13.9V but still with a battery light and a P0625 Generator field terminal - circuit low error present. At this time the old owner throwns in the towel so i buy the car. What do we belive the fault might be? need a new denos unit? faulty wire?

Any help is much appreciated