1998 GMC Sierra What am I missing

I recently rebuilt and installed the engine to my truck. After hooking up the positive side of the battery the starter to turn. I noticed that the wires were touching. I separated them and the problem stopped. However once I hooked the battery back up and tried to turn the engine over there was nothing. My dash lights will not come on as well. I have already checked all the fuses and the battery is good. I also checked the wiring harness and made sure everything was plugged in. Please let me know what else I can try.