Are you sure its a wire? From the picture it almost looks like part of the windshield washer fluid line. I hit a deer years ago and needed a new hood because of it, and when I got the car back i had a similar looking thing dangling around over by the cruise control. Ended up being the mechanics never finished plugging that fitting into a splitter under the hood, at the back of the heat liner.
I know the system uses clearish white fittings like that, and are located at that side of the engine bay...also, the reservoir is on the passenger side of the car, a little above the alternator...you may have yanked on it by accident when under the car...but can't tell for sure from the picture.