I'm having this exact same issue with the fan lever switch. I had to wiggle it to stay on, but now doesn't turn on at all. I replaced the resistor thinking that was the issue, but the issue remains. I took off the center console and looks like the piece below the lever is broken. Looks like I might need to replace my climate control unit, but haven't seen any DIY on it. So many cables, plus the hot/cold knob pulls a cable that manual moves the heater control valve. No idea how to unhook that.
Just recorded this today
2000 3rd Gen 4runner manual climate control - YouTube