OK..That was just a quick test for regulator circuit and motor verification..
Now , the yellow wire at the regulator is a variable voltage [ 2-7v] that triggers the regulator. Put the Defroster On high and see if you have voltage at the yl wire and ground.
This can also be done right behind the brake booster..there is a 3 wire plug that comes from the CC..
[ red/yl/blk]...you should have 12v from red to blk, and variable voltage from yl to blk.
If you do , then the regulator is bad ..is you don't , we have to continue w/other test.
Basically , when the reg gets trigger voltage [ yl wire] from the CC, it grounds the blu wire thru the regulator. It is a Switched Ground, but variable. The red on blower is always HOT and have nothing to do with speed regulation..that is done on th ground side of fan motor [ blu]....which is why I had you ground that blu wire ..that test by-passes the reg/CC circuits and brings on High Fan w/o regulator/CC in the circuit..