My car's a lot more junior than yours (87 190e). Check if your engine temp sensor is in order (I think yours is 3 pole geen).

1. Take it out, shake and see if it rattles. If it does, it's busted.

2. To check if the fan is working, unplug the switch and short the holes on the plug. 1 is ground and 2 connects to the fan relay which activates the fan. Of course do this with a fresh fuse.

Try step 2 first, since it's a lot easier to do.

Good luck.