1990 Chevy Silverado Loss of Power

I have a 1990 Chevy Silverado with a 5.7L V8. I am having several problems when the truck is in idle and while driving. They range from my radio turning on and off. To my blinkers blinking fast then normal. The gauges will dim and be allover the place or not read at all. The check engine, check gauges and brake warning lights will turn on. These seem to happen most when i shift the truck into reverse. The blinkers, radio and gauges seem to be when I push the brake or the door locks. But the other thing is that it might do that for two or three days then will run like a brand new machine the next. Thanks. Michael. Oh ya and if the brake light is on while driving the engine has a major loss of power and will barley make it up inclines.