Well this may me a couple of years late. But for all of you car owners out there here is the explanation for car tempered windows shattering. I have worked for an automotive glass manufacturer for over 20 years in both windshield,sidelite and backlite operations. In direct sunlight a backlite will expand in size about 1/4 of an inch. With our size tolerances of +/-
1.5mm and the body size tolerances you can get enormous pressure from a big window,small opening. Oops shattered window. Also and edge defect will do same thing. Small crack or chip couple years pop.On tempered parts you can drop a one pound steel ball from 20 feet and it will just bounce. Tap the edge and poof. As for fixing a broken grid line go ahead. The auto shut off is to stop the lines and soldered leads from melting off. Repair of leads and lines was a full time job in our plant. Only caution is use the lowest temp possible as you may just melt your lines more. Remember back and side windows are designed to break. Side rear windows that only roll down part way for child safety are vulnerable,watch what you are loading.