The wiring diagram in the 126 shop manual isn't very useful in that regard. It shows a coolant sensor input into pin 6/white wire. It also shows something like a potentiometer with words to the effect that as temperature increases resistance decreases with a reference ground at pin 4/brown. These wires are in the connector that doesn't contain the wires that go to the glow plugs.

Sixto
91 300SE
87 300SDL
83 300SD