Electric fan problems!!! Please help!!!

i took my car(2001 325i) to a mechanic and he said that i only have one electric fan behind the radiator and it's not turning on!!! It's receiving power up to an aluminum box that's on the fan!!! do i have to replace the whole fan or just that box?? What is that box?? Is that the fan switch(relay)???

What I believe you see is the auxilary fan (that is the electric fan) resistor. The resistor screws to the front side of the fan and is generallly the low speed circuit. This item coast about $21.00 US from online suppliers. You should also have a fan switch (really a temperature controlled screw in electrical switch) that has both high and low fan speeds. This device screws into the upper drivers side of the radiator and gives the elcetric an high and low speed signals. A Bentley manual gives you test procedures for all of these items.