HVAC problem/bad wiring

I recently bought this truck with various issues. The engine temperature gauge did not work (replaced sensor and still did not work). The sunroof is stuck open slightly, but motor works. And most frustrating was we had no AC/heat controls. The other controls on the HVAC control worked (hazards, 4x4, clock, etc) but not the HVAC and the lights did not light up (circled in first picture). I bought a used one on eBay thinking that would solve it and it also did not work. In my frustration I began unplugging the "new" panel and after removing one of the plugs (circled in the second picture) the lights on the panel came on and we had control of the HVAC. Also, as a result the temperature gauge works, and the outside temperature sensor also works. My thoughts are a loose ground. Any help/thoughts?