That looks like a ground wire, be very careful with those boxes, I have heard stories about people who had a dead battery and something in the computer became corrupted and it did not work after that.
Another thing that could happen is electrostatic discharge zapperoo, i have seen other electronic devices stop working after touching it without protection. that little spark from rubbing carpet, or a balloon.
As long as you dont put the box down, and take your hand off of it, it wont get zapped the next time you touch it, so they make a bracelet that has a wire attached to it, that always makes contact with your skin as you wear it, and the wire has an alagater clip on it, you clip it to the metal chassis of whatever your working on, and that way you never disconnect from it.
Remember to touch the metal of the car your working on, before you touch the box.