I don't know why I have never paid any attention to it before, but I opened the hood to clean the engine the other day and noticed that the inside of this connector looked a lot cleaner than the rest of the engine. The fact that it is clean makes me think something was plugged into it, but I can't figure out what.
I looked in the engine of a 98 Pathfinder to compare, but it does not have this connector sticking out next to the fuse box.

