I have a 86 420 SEL, and had a similiar problem, there is a metal blade fuse on the fender well on drivers side just behind the anti lock brake components, it is a black plastic 1" by 2" piece with a wire out each end. try this 79 cent fuse before you spend $300. like I did.
If thats not it there is also a component in the same housing as the fan, it has fins on it, it is part of the automatic climate control for the car, if it is bad it could cause the same problem, don't replace it yet "E" mail me at MPAFALCON@aol.COM and I would be happy to part with this new part for you, if it is in deed what you need.

good luck

[Edited by TIM PAULUS on 02-19-2001 at 04:07 PM]