Originally Posted by Zulfiqar

its no.2 sensor, it should have two brown wires - it routes ground power to the low speed fan relay to start the fans low speed.

I would suggest you first check the fan circuit by manually verifying the fans are good, remove the 2 wire connector held in a metal clamp and feed it ground and power, if they run you are good.

test the low speed circuit by removing the (sensor two wires) in your pic and joining them together (join the harness side) - the fans should run low speed, if they still dont you need to verify that you are getting voltage at the step down resistor that is bolted right next to the reciever drier, it is known to burn the wiring after the resistor.

If you still dont have voltage at the leading point of the resistor after you shorted the pressure switch wires then you need to check the fuse to the low speed, its on the relay itself which is in the relay panel behind the fuse panel in the fuse box. The relay is a blue one and has a 15A fuse originally a 20A fuse is accepted and recommended by MB dealerships to prevent short life.