On my '81, the monovalve connector is right on top of the valve. It is a small two wire socket that fits onto the plug on the valve. There should be no voltage on it when you want heat and 11 ~12 volts on it when the heat is off. Mine needed to have one wire re soldered to the connector. Try doing that. The blower should not come on right away after you stat the car. It waits until the coolant is 35 degrees C before activating. If you push the high fan button it will come right on. When you think it is going off it might just be going into low speed. In low it is nearly silent.

Hope this helps...

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Current
Monika '74 450 SL
BrownHilda '79 280SL
FoxyCleopatra '99 Chevy Suburban
Scarlett 2014 Jeep Cherokee
Krystal 2004 Volvo S60
Gone
'74 Jeep CJ5
'97 Jeep ZJ Laredo
Rudolf ‘86 300SDL
Bruno '81 300SD
Fritzi '84 BMW
'92 Subaru
'96 Impala SS
'71 Buick GS conv
'67 GTO conv
'63 Corvair conv
'57 Nomad