My 95 gmc turbo diesal.The battery light came on while driving next morning would not start and glow plug did not come on. Replaced both batteries after testing and replaced glow plug relay. Now non of the engine lights come on including glow plug. Exchange glow plug for another in case the first one was bad. Same problem no engine lights and non starting. Touched to glow plug wires together while key is on and glow plug light will flash on and off. Any suggestions Thanks