the fan switch is located on the drier assy. which is in front of the ABS unit. on my car the top is black plastic and has two leads with spade connectors attached. the other device next to it is the pressure switch(mine is green). this prevents the compressor from running when low on freon. You may also want to check the large ceramic resistor under the ABS unit. they commonly cause the aux fan to not work. Either way i would do some testing with an ohm meter to pinpoint the problem
01 ML55 AMG
92 500E (a few mods)
87 300E (lots of mods)
00 Chevy 3500HD Diesel Box Truck
68 18' Donzi Marine
06 GT i-Drive7 1.0 Mountain Bike (with GPS!
PREVIOUSLY OWNED:83 300SD, 87 420SEL, 88 420SEL, 90 420SEL, 86 560SEL, 86 190E 2.3-16V AMG, 94 E320