At least you are protected from random violence, maybe I should consider being anonomous. But, I am over it and I am sorry, so here is your answer.

The voltage given in the display is the control voltage. if you made the circuit into an amplifier transistor device this voltage would be the base biasing voltage. The transistor then would alow current to flow in proportion to the bias strength. Transistors are used as amplifiers or switches. In this case they are being used as an amplifier.

The voltage I was mentioning; the voltage drop between the blower ground and real ground is a measurement of the level of amplification. If the transistor was at high blow there would be theoretically no voltage drop as the ground of the motor would be pulled all the way to ground. In low blow the blower ground is only pulled to maybe 6v. The regulator/transistor looking like a resistor to the circuit.

The test is easy as the blower circuitry is easily accessible under the large plastic cover at the rear of the engine compartment. There you can verify that the bias voltage displayed on the pushbutton controller is the actual voltage seen by the regulator AND using the voltage drop method one can see how the regulator responded to command.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician