Ground wire was bad.
Fan works when both pigtails are jumped. Without jumping, only 100C coolant temp switch turns on the fan on high.
Therefore we can argue the high temperature switch on receiver/drier is bad.

Now the interesting part: the service manual claims it can be removed without evacuating the refrigerant.
New one comes with a rubber o-ring and seems to be a pressure switch...
Who's right?

https://www.startekinfo.com/StarTek/outside/12253/disc%202/program/Climate/83-532.pdf

The manual seems to talk about this: https://www.*******.com/products/mercedes-porsche-a-c-refrigerant-temperature-sensor-meyle-0008208010

While suppliers mainly sell the later "red" switch. I have to check which one is on the car.