I have a 1992 325ic. The air conditioning works fine but when I turn it on, the aux cooling fan, which should come on at low speed, does not operate. The fan also does not turn on when the engine gets hot. The resistor pack was changed in 2015 and the replacement (Magna) looks to be in good shape with no burning of the wires or the housing. Here's what I've tested: 1) When the ignition is turned on and when the AC is turned on, I disconnect the 3 prong plug from the temp sensor located on the radiator. Bridging across the black/brown and green/black causes the fan to run at high speed. Bridging across the black and green/black does not turn the fan on at low speed. 2) Swapping the low and high speed fan relays (K1 and K6) does not change anything. 3) Fuses 19 and 3 are showing 12 volts. 4) Fuse 18 does not seem to show voltage. This seems odd. 5) For grins, I ran jumpers directly from the battery (positive and negative) to the resistor pack leads ahead and behind the cooling fan. This is a black wire. there are 2 wires running to the fan, a red and a brown. If I connect the jumper to the resistor connector between it and the fan, it comes on at high speed (12 volts). If I connect the jumper so voltage needs to go through the resistor, nothing. No voltage and the fan does not come on. I've done what I wanted not to do until knowing what is wrong by ordering a new resistor pack and a new thermo switch for the radiator. It seems the testing I've done would have bypassed the thermo switch as part of the testing but this is getting frustrating and maybe throwing parts at the problem will eventually solve the issue. Does anyone have an idea of what may be wrong? I'd really like to turn on my AC with the car running and have the aux fan turn on at low sped. Any help would be greatly appreciated.