I tried your method, but I got no where. I even tugged pretty hard, expecting it to break, and nada.

My fuse box cover is clear plastic, and has a metal closure clip at the front and what looks like a metal hinge that engages a protruding plastic nib on the cover a few inches from the back. If I reach my hand over the cover and down the back edge, I can feel a slot or opening, but I can't pull upward as my hand is squashed between the cover and the car body at the rear.

I think I must be missing something because it is seeming a bit impossible to get to the big black relay back there. If I had to I could probably pull the two silver ones in front of the big black one out, but that would not guarantee me I would not be stumped anyway. There is next to no clearance above the rear most relay top and the bottom of the cover when the cover is as wide open as it gets.

I really don't want to break this thing, but will have to just go back to tugging at it. Thanks, Jim

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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)