After nobody has replied for some time now, I'll share my experience, but I'm not an electrical engineer: This alternator has nine diodes. Three pairs of three. I found that on my alternator, the two banks of large diodes checked out allright (using a Fluke meter). Still, the alternator did not charge properly: The red dashboard light would stay on at idle and at increased RPM's would go dim. The third set of diodes controls the voltage regulator. There are three connections on the voltage regulator and on the alternator (plus the power connection where the charging current is taken out). The three connections are maked D+, D- and Df. Note that MB uses the color brown for ground and black for positive. Therefore D- is the brown wire. You may want to verify that the wiring is connected properly. The pins of the regulator are also marked. Most shops cannot test the alternator properly i.e. they can only test the alternator for output, but not the third set of diodes which control the voltage regulator. My alternator tested just fine for output. Instead of having my alternator rebuilt, I obtained one from a scrap yard much cheaper. I feel that you cannot damage the voltage regulator with a defective alternator, but the voltage regulator has a relay in it with points and can certainly become defective. You can probably remove the cover and inspect it visually and using an ohm meter.The one from the scrap yard is a 55 Amp alternator, it is much more common and the same size. Try to find a shop which has a CRT display with the alternator test bench: Then you can see that all three legs of the alternator charge uniformly. I went to Blanchard Electric in Seattle.
'69 280SL,Signal Red,113044-12-007537,tired engineer, West-Seattle, WA
