Wire plug is probably for power/heated seats. Not rear defroster.

Does the on/off lamp on your defogger switch illuminate?  (Check with the
car running.  It won't turn on unless the car is running.)  If not, start
by checking your fuses.  If so, turn it on and go to the rear glass and
check to see if you have 12V between the two terminals.  If you get the
12V, you're looking at a grid problem.  If you don't, you're looking at a
problem elsewhere.  You'll probably want to get a schematic if that's the
case.

Most frequently, one of the wires is disconnected or the tab came off the
window.