Having just gone a few rounds with the regulator in my 500SEC, including digging up the diagram for the wiring in our alternators, and watching it with a scope, I found out a few interesting (at least to me) things about how MB did it.

If the diode bridge is functioning properly, it's a full wave, three phase rectifier.

When one of my diodes failed, it showed up initially as a charging system light glowing brighter with increase in engine rpm, as well as the brake wear light and empty fuel tank light.

Once I hooked my oscilloscope to the car to check the output waveform, I found that instead of the specified even ripple, mine had a sharp drop out on every sixth wave.

That being said, the 14 volt charging system check was at ~2300 rpm on my car, as the alternator just isn't spinning fast enough to be putting out full voltage until it's up to it's target rpm. The ETM had a list of different vehicles and their respective minimum RPM's for testing.

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-Josh
Testing the cheap Mercedes axiom, one bolt at a time...