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As your First post stated..............and I also know that b/c I have your schematic up on a wall here. That is how I diagnose over the net and why I have sequenced test procedures for you to perform while I am tracing your systems circuit out.

OK

I can see your problem is your understanding of "PIGTAIL"
Re-read my post warning notation about the difference between the 2 sensors on the drier.
A pigtailed sensor is a sensor that has a length of wire with the connectors on the end of that wire [ pigtail wire]..

So , your first picture is the sensor for the compressor and only has spade connectors. That is the one I posted not to use.
The aux fan sensor I wanted jumped has a pigtail lead with the connectors on the end [second picture ]

Here is the correct sensor:

http://catalog.peachparts.com/RenderScriptTemplate.epc?_cmd=epccat_VehicleAAA&cookieID=2GN17VPXQ2GQ0OFOTO&yearid=1989%40%401989&makeid=MB%40%40MB%40%40X&modelid=260%2DE%2D001%40%40260E&catid=R%40%40Climate+Control&mode=PA&subcatid=R1055@@A%2FC+Temp%2E+Switch&source=www.peachparts.com&clientid=catalog.mercedesshop

If one has a low fan jumping THAT sensor at the end of the pigtail ,[ which you now have concluded] then your problem is most likely the refrigerant level is slightly LOW, thereby not allowing the high side pressure to reach the cut-in spec of that sensor. Low fan ONLY runs when there is a high thermal load on the a/c condenser. The only other possible is a bad sw , but that is highly unlikely b/c low Refrig is a 99% diagnosis. If one sees bubbles'foam in the drier eyesight, you are low. [ or gauges on High side will tell]

OK
Back to the High Fan
Is this the sensor you have??

http://catalog.peachparts.com/RenderScriptTemplate.epc?_cmd=epccat_VehicleAAA&cookieID=2GN17VPXQ2GQ0OFOTO&yearid=1989%40%401989&makeid=MB%40%40MB%40%40X&modelid=260%2DE%2D001%40%40260E&catid=R%40%40Climate+Control&mode=PA&subcatid=R1075@@A%2FC+ACC+Temp+Sensor&source=www.peachparts.com&clientid=catalog.mercedesshop

__________________
A Dalton