The car is a 1992 400E. I have no response from the blower on the basic settings. I have removed the blower and it responds to a 12 volt source. Before I order parts I would like to know if there is a diagnostic procedure to determine if the problem is the push buttons(control) or the regulator. The blower is on the bench and the regulator is out. I do not get 12 volts output from the regulator, but there is 12 volts into the regulator. What is the best way to determine the function/correct response of the yellow wire into the regulator?