Hi,
If the light isn't turning on, either there is no connection at the grid or the switch is bad. I did find a few technical service bulletins related to grid connector tab failure and how to repair it.
Do me a favor. Check where the grid plugs in and confirm the tab isn't damaged. Also, I want you to take a test light and check to see if power makes it to the grid. If you look at pic 1, it shows what happens to the grid connection.
If you find the test light does turn on, then there is a connection issue at the grid. If it doesn't turn on, move to the switch, and confirm there is power both to it and out from it. If there is power in and not out, replace the switch.
I attached two more pics showing the entire wiring schematic for the rear defroster. I had to cut the pic in half to make it readable. It shows a purple wire going to the defroster so make sure it has power. Also, I realize you checked the 40 amp fuse. Make sure power is both in and out from it and also check the 10 amp fuse highlighted in pic 2.
Here are a couple links you may find helpful:
https://www.2carpros.com/articles/how-to-check-a-car-fuse
https://www.2carpros.com/articles/how-to-check-wiring
Let me know what you find.
Joe
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Sunday, December 20th, 2020 AT 10:08 PM