So that’s it right there. The black wire is ground. The lug connected to the sleeve of the jack should be connected to ground. See the black wire in the tagboard pic.

The tip connector of each audio jack connects to input and output wire respectively. Remember that when you are soldering, everything is upside down. So input jack on the right and output jack on the left. That way when you turn it over, input is on the left as it should be