It's not listed in the Service Manual, nor did a google search turn up anything.
You'd likely have to take it completely apart, and trace out the schematic by hand. 😱 I assume you have a DMM and Oscilloscope. 😉
For pin-outs, you could try to obtain a schematic on any PSU, as the connections would be the same. From what I can tell, the Mac Pro doesn't use anything weird. 🙂