i was thinking about getting a new rear windshield in the future, and i really would like to have electric defrost on it if i replace it. my car did not come with electric defrost, and i was wondering (since my dad will end up making a complete new harness for the car anyway) if i could run a switch and relay only on when ign. circuit is on to the defroster. is this a safe way? is there a better way? is there a way to do it with a timed switch? my dad said the reason they have a safety timer from the factory is because they would crack windshields if they were left on too long.