Help with rear brake lights wiring harness.

[NeoJuice]

So the harness for the rear of the truck was not connected when I bought it and was in a box in the back of the truck. I finally snagged some tail lights and want to get it hooked up. Having a little trouble determining what a missing wire is.

I found the plug under truck and the end of the harness. My question is.

What is the broken wire? I'm assuming it's a ground wire that's missing end on it. Also you can see on one end of the wiring harness there is no ground and on the other end there is a ground wire by the light sockets. So should all I need to do is put a connector on the clipped off wire and should be good to go?

Any help would be appreciated.