I respectfully disagree, the voltage should only change when the dial setting is adjusted, ie from a setting of say 2 slow speed, up to a setting of say 5 full speed. Random changes in voltage to the PWM (resistor/regulator) via the pink wire would cause the blower motor to run erratically, just as we are all seeing.

The voltage should be constant for each dial setting. I however confirm that I did not make it clear that my comment (item 4) was to state that the voltage was fluctuating without any change to the blower speed dial setting.

Kind regards
Mark