Originally Posted by hey_allen

I just had an oscilloscope on my car's output to find that I had a failed diode.

The reason I mention it is that there wasn't all that much variance in the voltage, probably due to it being a rectified 3 phase sine wave. With that many phases, and since it's rectifying both the high and low sides of the sine wave, you end up with a fairly smooth waveform on the output. (At least you should if you don't have a diode out, causing a huge valley in the waveform!) Picture HERE