Wiring Gremlins

My dad bought a 1991 Dodge Ram 250 4x4 with the 5.9 cummins in it. The truck was wrecked but we have fixed it back up all for one thing. We hooked everything back up on it. The truck starts fine runs good but everytime we try to move it the guages flicker and everything goes dead but the motor. I thought it was something in the steering wheel because sometimes when you turn the wheel it would kick back on. Also sometimes when you mash the brake it would kick on and off. I checked all the wiring for shorts and found nothing. I put the steering cover back on and thought it was fixed because everything worked. I backed up 5 ft and everything went dead again. The motor wont shut off either when it is messing up. I talked to a local mechanic and he said it was the computer gone bad. He said he had to replace a computer on one because it wouldnt charge and he called the local dodge dealer and they said computer bad. He told me when he replaced the comp. the truck charged. Maybe the computer got damaged in the wreck before we got it? All i know is that i cant drive the truck at night because of this. Also when the wiring is kickin back on all the relays go off i can hear them flickering. Any help on this will be greatly appreciated