Smoke from under the dash

[67cruiser]

67 C10 I was having headlight problems, pulled the headlight switch traced out the wiring to my bright switch on floor panel. Believe I had a loose connection down there recrimped all 3 wires, put headlight switch back in and headlights worked. Turned the knob to check instrument panel dimmer (ccw rotation) and smoke started pouring out from under my dash. Noticed on switch when it is turned all the way CCW it pushes down a contact and grounds it not sure what that does if for dome lamp ground or what. Ran out of daylight before I could pull switch again. Any help would be great. Also have a vibration problem when I get going above 55mph. It starts shaking the cab not real bad but very annoying. Somebody told me start with the U-joints, does that sound like the problem.