I just performed this modification utilizing Mercedes parts and added an external 30 amp fuse holder with 30 amp blade fuse to my blower motor circuit on my 85 380se. Mercedes did this starting mid year 86 on all S class sedans. My mid year 86 300sdl had it installed from the factory. I posted the procedure a few weeks ago. Search under my name and I described the part number and the procedure to follow. It works very well.

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John
1986 300sdl
1985 380se