How to change LCD cable on chromebook c43-431 and leftover black wire?

My high school son uses an Acer Chromebook 14 CB3-431. Great system, the ids are locked down in a google group. The system ran fine for 3 years. Then the screen started showing about 1/3 of the lower area covered in random horizontal lines. When plugged into an external monitor the display was good. I decided the LCD or the wire was going bad. So I watched many videos on changing the screen. No big deal. But I didn't find any video on replacing the wire. So I took it apart an inch, and put together an inch. I thought I had everything just right. I got almost all of it back in place when boom, there is a black wire with some solder on the end not connected to anything. Crud. I can't find a hardware spec. Anyone know where this wire goes?