Welcome to the world of rebuilt electrical components, third world working on first world devices, trained by no one, with no quality control measurements, much less any accountability.

Quality Control: "We don't need no stinking checker. If I say it's good, it's gets boxed and shipped!" :

They only bench test and replace hard failure components. No one is load testing anything.

The only way to test Alt out put is to load test to specific AMP value and read voltage,total amp output, and diode results. Reading volts will show regulator control/alt output but not total capacity and capabilities of the said unit. Testing must be done at 1500 RPM and again at 2500 RPM.

The cheapie rebuilt unit issues with poor/ inconsistent output are legendary all across the industry. If you are keeping the vehicle go with a new unit and save yourself a lots of grief.

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2005 X5 4.8IS
The Blue ones are always FASTER....

Current Garage:
2005 X5 4.8is
2002 M5 TiSilver
2003 525iT
1998 528i
Former Garage Stable Highlights
2004 325XiT Sport
1973 De Tomaso Pantera, L Model
1970 Dodge Challenger T/A 4 sp Alpine White
1970 Dodge Challenger T/A 4 sp GoManGo Green
1971 Dart Sport, “Dart Light” package
1969 Road Runner 383
1968 Ply Barracuda 340S FB Sea-foam Green