O.K.
The auxiliary electric fans are activated two different ways:
1.Engine OverTemp. (I believe this sensor is screwed into the housing at the
top of the head where the top radiator hose attaches))
2.Refrigerant OverTemp. ( #292 in the Pictogram)(Screwed into the Reciever/
Dryer)
#295 in the Pictogram is the Series Resistor for the Fans (White Ceramic holder behind the Driver's Headlight.)
12 Volts Positive to the bolt on the rear gives you low speed fans.
12 volts Positive to the bolt on the front gives you high speed fans.
[That will tell you if the fans and the resistor are working]
There are also Two relays in the relay section of the fuse box(Behind the fuses)
AND a couple of fuses
The Engine Overheat sensor MAY not even activate until engine temps reach
105c,depending on which color sensor is used.
EDIT: This is the only source I know of for ordering the FSM on 2 CDs for
the W124 chassis:
http://www.mercedesmanuals.com/Mercedes_Benz_W_124_Manual_p/w124.htm