I recently bought a car and the rear windshield defogger is damaged, by which I mean the heater that works by wires on the glass, not an air blower. About 5 of the 10 wires have long missing sections where they have come off completely. These are on the lower half of the glass. I've looked into paint-on products but they get bad reviews and can only be used for tiny areas of damage. I might be able to save one of the wires this way, which has only a small area of damage. Other options include buying a kit to install a whole new unit, which involves scraping off all the wires, or getting a replacement glass or even tailgate from a scrapyard (would they even test it was working?). I am wondering, do auto electricians do this kind of repair? What might it cost? I can manage with half a defogger but it's a bit annoying.
Your options in my order of preference:
source a replacement screen or tailgate which has the heater wires in good condition.
use the conductive paint to repair the damaged sections - I have done this for sections of 8" to 12" with success but depends on the quality of the paint, having a clean surface and using masking tape to get a clean edge.
purchase a replacement kit but those are not usually matched to the screen size very well. Cleaning the glass is again important.