What is this?????

[SubaSteevo]

I was installing new headlight bulbs and I found this thing laying next to the battery, not attached to anything, just laying there. I was like "hmmm....I wonder why that's there" so I went to see what it did and the thing pulled right out. I have a couple of questions, 1. WHAT IS IT?, 2. where does it go?, 3. what does it do? I dunno if it's important or what but it definately didnt belong where it was.