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Thank you for allowing me to help you with this concern today and am sorry to hear that this is happening. For starters, I am assuming that you will be doing the repair yourself. Do you happen to have a DVOM or Multimeter to test for voltage?
Ok, turn the defroster on and check for voltage at all the lines on one side and then the other. On one side they should read about 12Volts and on the other it should be much less(maybe 1-2 volts).
New expert here. Your black probe of your voltmeter should go to any clean metal surface. While in the back of the vehicle that can be a little difficult with the door closed. The other option is simply use your voltmeter and scratch very carefully a little clean spot on the long vertical grid on the left and then on the right. When your voltmeter is across the entire grid you should have plus or -12 V. Depending on how you have the probes attached it may read reverse polarity. Your meter will compensate for that it does not matter you're just looking to see if you have voltage to the grid.