If you're having a problem with your auxiliary fan, you might want to check out the fuse.
All summer long, I've had a probem with the fan in my 84 380SE. Been reading all of the information in this forum about the fan, and I guessed I was facing a bill of several hundred dollars. So I put the fan problem on hold and suffered. When the temp gauge hit 100, the air conditioner went off and the windows came down. And I suffered.
Well ... yesterday, I followed the advice of somebody in this forum and pulled the fuses and sprayed them with electrical contact cleaner. I figured some had gotten a little corroded over the past 19 years.
Got to the last fuse, and lo and behold, it was broken. I checked the diagram, and guess what. It was the fuse for the auxiliary fan.
Replaced the fuse, and the auxiliary fan problem is solved.
Moral: If you're having problems with the fan, check the easy things first ... things like the fuse.
I hope this works for at least some of you.