Morgan Freeman Narrator: There were breaks in the conductive material.
But srsly, it's not a complicated system. There are two electrical connections on the window, current goes in one and grounds through the other. And heats through resisance as it does so.
if some areas aren't heating, it's because current isn't flowing through them. And if it isn't, it's because the conductive material is broken.
You can test this with a multimeter, set it on 20V DC, ground the black terminal, and then *GENTLY* probe around on the grid. I'm not sure which side is the 12V+ and which side is the ground, but you should be able to tell on the working part. And try in lots of places as you move up toward the non-working area.
The way the gird works, if you're missing a whole upper section, it's likely going to be a break in the vertical lines that bring the current up from the connectors on the bottom edge. There are fairly short sections between each horizontal 'heater' line.
Individual lines not working could be a break anywhere along the horizontal length of a line.
