u can buy the liquid conductor paint, they suppose connect 2 broken circuit together u touch up where the sparks occur , i bought a bottle from wal mart few yrs ago, but never tried it. if it didnt work u have only wasted 10 bucks. is hell lot cheaper than a new glass.
or connect a 12v elec computer fan on the rear shelf, its going to do the same. if u're old enuf these were standard features in the big 3 cars during the late 60s to 70s.
we can even buy a plastic filled with these heated wire and glue her to the rear window during my hey days.

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