does anyone know what the aux fan diode is for? Where is it located? I see many bmw parts stores listing the aux fan diode, but i do not know what it is or where it is in my '84 318i. I was wondering if a failed aux fan diode be preventing the aux fan from switching into hi. i've jumpered tested and replaced the thermo switches and verified that the relays and fuses are good and replaced the aux fan resistor and tested the wiring. all is good, but i cannot get the hi fan to initiate. i hear clicking like when i jumper the lo speed wires, which tells me that the fuse/relay is getting the signal. if the diode is somewhere in the line of the aux fan trigger line, then i was suspecting it to be the problem. any comments welcome. thank you.