560SL central and foot flaps

Dear all, 

My dashboard is out for crack repair
and it is a time to repair problems with vacuum elements. 
Everything is done: changed vacuum membranes, 
repair cracks on plastic of heatbox, checked vacuum leaks, but fresh air, central and foot flaps don’t work. 
I found value theme for repair of pressure valve Y34. It is on my desk already and found out the circuits 2 and 4 don’t click when apply 12 V. Also circuit 1 ( for foot flaps) 
is sealed with yellow plug. Should I open that plug? It looks like original, maybe is something common for USA cars?