I have a 2002 Corolla GS. Rear window defroster not working

The main cause for the rear window not working is a disconnected wire at either side of the defroster grid. You can see where the body harness connects to the rear glass.

The second most liekly cause are broken defroster grid wires.

I would suggest to you to obtain a 12 volt DC testlamp, and check for voltage as follows, at the rear defroster.

Hook the clamp of the testlamp up to a known good ground. The back door latch 'hoop' is great. Next, turn on the rear defroster, and place the point of the tip on the extreme side of the back window, on the grid. Does it the tester light up bright? If not, try the other side.

The light, moving across the grid, should get noticeably dimmer, if the grid is functioning properly. The light will go out when you encounter a broken grid wire..