The black wire by itself seems like it is disconnected from somewhere, but after looking at the photo, no immediate location, since the wiring is tie wrapped it can't be far. One likely culprit to consider are the continuity of the DPDT switches when they are clicked from up top, A cheap multimeter on 200 ohms scale will conclude the continuity of good mechanical contact to ensure a signal path. DPDT meaning double pole double throw switch basically translate to center to either side of the leg when clicked. Should a missing signal path exist on a switch, soldering a replacement will need to be done.
One thing to consider, soldering one lead on DPDT terminal isn't too bad, but should wiring require two wires to connect to the same terminal, that gets requires them to be twisted together then soldered to the point.