Haha right on. Did the same thing when adding a resistor to the aux fan temp sensor on the m103 head to engage the fans at a lower temp.
Was wondering if you got fancy and found those 3-way female to male pin Benz clips to make it a plug in play type thing. I think those type of clips can be found in the interior passenger floor area of w124s... The official MB harness for testing the EHA uses a similar type clip but last I checked those harnesses are $80~ thereabouts lol. Now that I think of it I guess this would only work with 2-pin connectors and not the 3 pin pot clip, but shoving the wire in works just as well
Got your PM about the Arduino monitoring. I def want to add this type info display, would be super neat. Still like the idea of your fan controller as well.