After spending the better part of last week going over my workshop manuals, testing my charging system components, reading all the posts I could find here at XS400.com and watching no end of YouTube videos I finally ran into a buddy who knows his way around a multi-meter and electrical diagrams. He came over and we went over all the readings again.
The first thing he noticed was that my multi-meter was off by .6 or .7 ohms. So when the resisitance across my stator wires should be .72 ohms and it read 1.4 ohms I didn't know what to make of it. Now of course, I can just take the variation into consideration but I didn't know that before. OK, so my stator and field coil are both good.
I didn't need to take variation into consideration so I was able to reliably test my rectifier and found that one diode is shot.
Here's the next zinger: I have both a Yamaha workshop manual and one I printed from here at XS400.com. Both have misprints in them for testing the regulator. I know nothing of these things and only knew I was getting readings that weren't making sense. When my buddy took a look he immediately knew that the test descriptions had been switched.
Here are the two books and what they say:
Download
Yamaha- bilingual Canadian version
Although the readings they say you should get are very slightly different the big thing is that the boxes with the readings are under the wrong instructions.
At the top of the description where it says to test across the black wire and the regulator base, the results should really be under the next test, where it instructs to test across the other two wires (either black/red and green or brown and green).
Once that was straightened out I was getting the proper readings of 142 ohms between the black wire and the base and 10.2 ohms across the other wires.
These are the workshop manuals for the 1976 XS360. I wonder if the XS400 manuals are similarly misprinted and how many other guys have been frustrated by whacky readings on their regulator tests. Did I miss the post that points this out to everyone so I'm the last guy to know?
I'm just glad I have a bit better understanding of the charging system now. So much frustration does lead to digging in and learning something valuable. My new rectifier regulator combo is on order.