124 Climate Control Blower Failure

1992 400-E I have no blower in any combination of possible settings of push buttons & temperature control thumb wheel. The fuse in the fuse box is good, the independent fuse mounted on shock tower is good. Now three pin connector in back of brake booster... I'm aware that the red wire is +12 volts...the yellow wire is 1 volt to 6 volts depending on the setting of the PBC & that the blower regulator switch completes the circuit to ground & the wire from the independent fuse on shock tower is + 12 volts originating at the ignition switch and provides battery voltage to blower motor. This I gathered from the info on this site. I have 12 volts from ignition across fuse to blower motor but I have NO 12 volts red wire at 3 pin connector behind brake booster. So this tells me I have an open circuit in the 12 volt supply to PBC or I missed a fuse. I do not have a circuit diagram so I'm not sure if the red wire originates at the fuse box. I would appreiate your help in determining if my analisys is correct. thanks & this is a great site MB Works & all involved. If anyone has a wiring diagram theyed like to share it would help me get this problem solved. My wife drives this car to work everyday and its cold in KY. MB Techs do I have this circuit correct ?????