My fans failed to turn on about a week ago with the A/C. They did turn on with the temperataure though. The only thing that I did to save me money and time was run a wire from the A/C's temperature switch to the fans relay. I ran it to the ground wire of the relay, now when I turn my A/C on about a minute or so later the fans kick in at high speed and shut down when the A/C cools again and so forth. And they also turn on when the engine is getting hot too. The relay is the first on or the second one in back of the fuse box in the drivers side of the engine. There's alot of relays so first or second to the left of the box towards the passenger side.
92" 300E