Another diagram I have shows the switch as B10/8, strange that the diagrams are the same other wise and the theory is the same.
You do not want to test this with the sensor disconnected as I suspect the controller recognises this as a fault and turns the fan on as a default (by grounding the relay). I do not know the resistance of the sensor but if its like most engine coolant sensors the resistance will be around 300ohms at around 80deg C.
The inside pushbutton controller does have self diagnostics. The codes can be gotten without special tools. You will need one of the following tools to do this; a logic probe, an LED, or a DSO (scope). If you can handle and have one more more of these items I can tell you how to do the code retrieval.
BTW the code manual for that model refers to code 12 and 13 as being short and open circuits in the B11/8 temp sensor. Strange!
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician
[This message has been edited by stevebfl (edited 04-11-2000).]