<< If so do I assume that if the red is bad it is the regulator?
>>

No,

The blower speed is controled by the regulator, which is triggered by the yl wire voltage . It is a switched ground... meaning the blower is always fed 12v on the hot side [+]. The reg. switching is done on the ground [-] side.
So if you have variable voltage at yl and no speed change with yl variable inputs , the reg is bad OR you can have bad bearings/brushes on the motor.
B/C the ground side is switched . all you have to do is ground the Blu wire at the motor and you should see FULL fan .. if not , motor is bad..[ grounding completes the switched ground circuit and eliminates the reg from the circuit]