If I have time I will go back to the shop and look at the diagram again, all my comments now will have to be from memory.
The S25 switch in the diagram is a two-fold switch in 86-87 after 88 I interpreted the diagram to infer that only the 115deg side of the switch was used.
The B11 is a variable resistor type sensor and keeps the control unit apraised of the engines temp all the time.
I forget the program but the controller starts altering the A/C cycle rate at around 105deg. At 115 deg the A/C is shut-off and the high speed fan comes on. I think both sensors take part.
Since you have a ground to pin 85 relay K9 you need to find out why the controller is asking for the fan. Unfortunately disconnecting sensors to the controller could initiate a fail safe type "limp home" strategy. If the controller sees an open circuit it likely will realize it to be wrong and it will substitute. In the case of something as critical as engine temp, it may just default to the fan on position.
Locating temp sensors on these motors is tricky as there are a number of them and their functions often change by the year model. The best way to test them would be from their input position to the pushbutton controller, it also allows checking the installed circuit. The problem on temp sensors is often the connetion itself. If you disconnect and check with an ohm meter the test may temporarily fix the problem leaving you no where.
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician
[This message has been edited by stevebfl (edited 04-08-2000).]