My '91 M103 has a 4-pin sensor on the far back of the head, just above where the intake runners enter the head. going in a circle, pins 1&3 are one temp sender, and pins 2&4 are the other one. Don't know which one is the temp gauge and which is the ECU signal though. But you could pull the connector socket loose and hang a 1K-ohm resistor between the wires going to 1&3 or to 2&4 and see if the temp gauge reads about 40 degrees C. Then you will know by default which two pins go to the ECU.
Each sensor should read approx 2K ohms at 20 c, and 300 ohms at 80C.
Hope this helps, I couldn't find a schematic that specifically identified the pins.
Of course, yours may be totally different.

DG