I didn't measure in series, but put the leads on the positive and negative terminals of the battery. I changed the alternator out this morning, and you are correct, I see the same cycle of numbers with about a 38V peak. I'm not sure how there are so many you tube videos showing the same test with completely different results, unless it is, as you said due to the accuracy of the autoranging feature.

So it appears the diodes in the old one were just fine. The bearings were shot though, and the new one is much quieter. The DC voltage is now 14.5V which is much higher than before, so the brushes were worn out as well.

I'm still scratching my head on the amperage reading. The first thing is I have to clamp it to the positive and negative wires to get any reading at all. I thought the clamp was only supposed to go over the positive wire. I have it in 400A DC mode. But either way, it still read in the mid 50s so that must be the max amps the car uses at full load. The textbook made the assumption that all cars must pull as many amps as the alternator is rated for.