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

 

Time to do some basic diagnostics. Start by checking all of the fuses, both in the engine bay and inside the cabin. Replace any that are blown. I'd also check and clean the battery connections. Follow those battery wires and see if you spot any problems with them. Are they cut open or exposed anywhere along their length? Follow the battery ground wire and check/clean where it grounds to the body.