2002 e39 charging problems

[superkev]

OK I have relpace my alternator twice (remanufactured Avanced Auto)
due to a dischaging problem. Initially the voltage across the battery reads 14.X V running. In 2-3 minutes after starting it drops below 12V. I have a new Battry 2 months. All the electrical check done on the car shows... Good Battery, good diodes, no output from atlernator. I've persued the theory of "unloader relay" but I don't know where it is. I have looked at all the gound connections and tested resistance in the positive cable to the battery and from the alt-engine-frame-neg battery terminal. I don't have a wiring diag for a 2002 E39. The car will run for ~ 2 hours before the battery gets too low to start. Once it went into the "trans safe" mode. I had my original alternator bench tested and to was good @ 13.8V diodes were good. I don'twant to get screwed by the dealer.
What can I do next?
Cound the OBC tell the system not to charge?