Electric fans on radiator not working 1989 190E 2.6

I have checked the fuses and the fans are good. They run for 2-3 seconds when you start the motor. It starts to overheat when sitting at a stop light. I can't find the relays that control them and I don't know where the tempature control sensor is that controls them. I think that it might be the ignition switch but I'm not sure. E-mail me if you can help. E-mail address is: trigg24@houston.rr.com

Thanks, Trigg24

[Stan Pittman]

The auxilary fans work for two reasons to cool the engine at high temps and for a/c high temps. There is a 2prong blue colored switch on the intake side of the cylinder head starts the fan for engine high temp. There is a switch on the receiver drier to also start the auxilary fan. The most common fault I've seen though is the resistor located just below the receiver drier. Check the continuinty of the resistor or check if it has voltage to one side and the other