iceref63

This is going to be a long one so please bear with me. I have a 2018 Silverado 5.3 that the motor was pulled and the DOD kit put it. Motor is back in the truck but no electrical power to anything. Battery shows 12.6 volts with no cables connected, 12.6 volts when the one positive meter wire is connected to the positive post and all 4 accessory posts with the negative meter wire is connected to the ground cable (not attached to the battery.) Once I connect the negative cable to the battery, it arc's a little bit but get no volts either between the battery posts or the accesory posts). Pull the negative cable off the battery and now hast 11.6 volts. This drop occures within 30 seconds. When positive and negative cables are connected to the battery, I get nothing, no interior lifts, no dash lifts, nothing. Thoughts?