I just got my first Z31 yesterday and loaded it onto the trailer fine the guy I bought it off took his battery out and i went to buy a new one. Got home all ready to go ripping around once I put the new battery in, long and short of it is I installed the battery backwards and after about 5 seconds there was smoke coming out of the small box beside the battery. I quickly broke the connection and now the car will attempt to start over but I have no electrical systems working besides the radio. I will attach pictures later on today. I just need help identifying what the issue could be, Thanks

 

Check the fusible links , 120 amp fuse
but it likely damaged the FI Ecu
we had a salesman take out 3 cars ecu on a cold day when they had to use the jumpbox on cars