You can't see where the latch catches on the fuse cover because it catches down below the latch. You simply drop the "catch" part of the latch down and then press the "handle" part of the latch towards the cover. Mine is really easy to press into the latched position so it's hard to tell that it really latched. It's also easy to flip the latch upside down so the catch is up instead of down. The it won't work. Maybe that's your problem...?

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84 300SD running on WVO