You must have blown the fuse on the positive battery cable. Time for a new one and this is why you're supposed to remove the cables when doing a plug change on these cars. It's going to be expensive.
2015 Mustang GT Premium Sold
2011 Mustang GT Premium Sold
2003 Mach1 Sold
2.3 Whipple, fully built motor with all the bolt-ons 718 rwhp/735 rwtq Sold