Ashnel06

I recently replaced the alternator in my grandparents 2003 infiniti i35 before hand they were getting problems where the vehicle would start up and soon after just shutoff so I guess they figured it was an alternator problem come to find out after replacing the alternator we get no power to the key fob, dash or headlights 100% dead no power we have used a new battery new 80a fuse for the positive connection still nothing. I have been told it could possibly be a bad ground wire but wanted an opinion from somebody that would know this type of car more any responses help, thanks