Chevrolet - Tahoe :: 2004 - Front A/C And Heater Stopped Responding To Level Knob

I have a 2004 Z71 Chevy Tahoe with 192,000 miles that runs great. The issue I have though is the electrical system is going haywire (no pun intended). The front A/C and heater stopped responding to the level knob, therefore doesn’t blow, the dash lights will periodically dim and go off, the horn doesn't work when I want it to, and the A/C would sometimes blow warm air when it did work. The A/C used to work on all levels of the dial, and then over time, level by level, they stopped working; however, the back blower works well on both A/C and heater, which is operated by the overhead control knob. I open the front vents to allow outside air in, rather than recirculated air, and the air coming out of the vents is A/C air, but it only blows when I'm driving of course.