I took a look at the link Arthur Dalton posted, which is a link to an online version of the MB Shop CD. Sadly my internet is very slow where I'm currently staying so it's difficult to view the pdf file since it's 73 megs.

My car has never has a cell phone wired to it.

From what you just posted it a seems as if the mystery box might contain both the aux fan fuse and the cell phone fuse. I took a look at wiring diagrams for the cell phone and the aux fans and they both seem to share the F22/2 box and the F1 box which has a 16 amp fuse relay.

Upon further looking under the hood I think I may have located all of the four fuses outside the fusebox. As already stated the blower motor fuse is located on the shock tower and is a 30 amp fuse. Located to the right in the picture is a 25 amp fuse which I think is for the heated seats. Not in the picture but just below it there is a 15 amp fuse that is of the newer plastic Japanese style, maybe the aux fan. And finally to our box it might be either the aux fan fuse or the cell phone fuse. Since I found it with a white 8 amp fuse in it, it would seem as if it would be for the cell phone, the wires coming out of that box are red and red/white.

This doesn't really seem to make any sense to me but I'm thinking that the fuse we're trying to locate might be to the cell phone, a while ago I had some weird problem behind the stereo where a wire burnt and was blowing the stereo/windows fuse in the fuse box, it was hot even with the ignition off. Maybe the cell phone wiring is screwed up and this is it.

I have no clue why there would be fuses in the car for both the cell phone and the seat heaters but maybe all the wiring is put in anyway and they just leave out the actual option itself, seems that way.

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1992 Mercedes-Benz 400E
2002 Mercedes-Benz ML500