Post 8 tells you that the CP show trigger voltage at the CP..it does NOT tell you if there is voltage at the yellow wire at the regulator.

The test is to check right at the regulator for 12v from red to blk and trigger voltage from yellow to black.
If he is grounding the blower motors blu wire and that gives full fan, then either the reg. is bad, the reg does not have proper feed , or the reg is not grounded.
Having the CP detect voltage output at the CP does not insure one has voltage at the regulator. Specially considering that he has already changed the reg and grounded the neg side of the blower, getting full blower.
My guess is the reg is not grounded...........but I would do the voltage check at the reg plug first.