Does the auxiliary fan kicks in as soon as you turn the car on, and wont go of? I had the same problem and the cause was a temperature sensor on the head which is linked with the a/c and the auxiliary fan. It is the sencond sensor from the fire wall ( I'll have to check on the location). I think I didn't dried the car well enough and short it out. Also some other problen arised from that, which I can not remember but got fixed a few days later after, I think it was the a/c relay behind the battery. Anyways it got fixed when it got dried a few days later and I tried not to mess with it for that time.

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'86 300E
'87 300SDL
'92 190E 2.6