Layback suggestion of steaming up the window is good. this way you know if the whole Grid is working.
I have a spare window I was thinking of steaming up and applying 12v directly to it to see if the whole Grid works.
There is/was a kit with the paint to touch up any Grid lines that do not work.
The HF DVM is easy to get for free. just look for their sales flyers and there is always something for free. One being a DVM.
I now have 26 sitting on a shelf.

Hey, they are free.
this is not counting the ones I have in the vehicles and gave away.
Charlie