1989 Chev Truck won't turn over, no power to dash.

I accidentally posted this in the Buik forum -- appologies. I have a 1989 Chevrolet K2500 Silverado, 5.7L throttle body, approx 100K miles, auto trans. My guages started jumping, brake and seat belt light started flashing, and engine began stalling when coasting. Stepping on gas stopped problem temporarily. Problem seemed to go away and then after hitting a cattle guard, the engine quit. Truck won't turn over, radio and heater/air conditioner don't work and instrument panel doesn't appear to get any power. Checked all fuses, none blown. Speedometer is stuck on 30 mph. But, headlights work, highbeam switch on blinker arm works, hood lights and interior dome light works. Any help will be much appreciated. Thanks!