I think I figured this out for my car. From reading here and testing the output from the PBU at the plug behind the brake booster. I verified that the output voltages going to the regulator were within spec according to the FSM and here, so the PBU is likely OK. I then jumped the ground contact(where the blue wire goes) to the battery negative, didn't touch the red, and then turned the ignition to acc2. Result was the Fan blew at high and that probably the regulator was bad. After reading here, that seems to be the definitive test to see whether its the fan or the regulator. I followed the Blower Motor removal Wiki to get to the blower and then posts here to that point.

PeachPartsWiki: Blower Motor Removal

It is sortof the chicken vs the egg on which part it is, so now my car is down while I try to source a regulator I have a W124 so yours maybe different.

Treetops