Vintage Cars: Auxiliary fan, coolant temp, ill answer

Question
QUESTION: Ron-
Good Morning, I have a 1975 450slc, I am looking to fix the auxiliary electric fan which is good, what controls it, also looking for a wiring schematic to trouble shoot and repair this.

Thanks for any advice you can offer,

Gerard Lowry
Palos Heights, Ill

ANSWER: that is controled by engine temperature or by turning on the AC.  DOes the car have AC?
I will look  for a schematic and let you know what I can find. One thing you can do is trace wires back from connection , brown is ground in Mercedes,

---------- FOLLOW-UP ----------

QUESTION: Ok, it's controlled by engine temperature  and yes I do have ac, the brown wire goes to the thermostat housing with the sensor, how does the sensor work normally open/close and then from there what does it do.

Gerard Lowry

Answer
MB designed the aux fan to run under two conditions:
1. >100C coolant temp at the aux fan switch on the water neck
2. >62C refrigerant temp at the reciever drier intake.
Both conditions require ignition accessory power at I think  terminal 15 (ingition switch postion I or II).

perhaps your sensor is bad, I beleive it is open when cold, closes when the temp is reached ,and yes it is a single pole switch