OK..now I get it.

So, take the switch on the drier with the 2 6" pigtail leads and unplug one of the leads..if the fan stops , you have a bad sw [ staying ON]


I just had to do some changes to this post b/c I noticed your car had some a/c sw version changes ..

..so, look here and see which one you have

http://catalog.peachparts.com/ShopByVehicle.epc?q=1977-Mercedes--Benz-450sl-Climate--Control&yearid=1977%40%401977&makeid=63%40%40MERCEDES+BENZ%40%40X&modelid=6278%3AMBC%7C1537%3AED%7C10000065%40%40450SL&catid=242213%40%40Climate+Control&subcatid=242240@@A%2FC+Temp%2E+Switch&mode=PA

__________________
A Dalton