But you can repair most cracks and small holes in plastic headlight or tailight lenses right on the car in minutes. You repair them by filling cracks with about 25 cents worth of almost any Liquiglas repair resin. Some like the thin Liquiglas chip or crack resin and some like the thick Liquiglas Pit-Filler. Whatever the resin, to prevent it from dripping on the halogen bulb, build up the crack gradually, partially curing each layer of resin in the break with ultra-violet or sunlight. One worker reports that feeding resin into a crack from a black syringe in direct sunlight causes resin in the crack to cure as fast as it is applied.
Quick cure means that much less chance of resin falling through the crack and hitting the bulb.
Narrow cracks are easy to fill, but large chips or holes are difficult unless the hole can be covered on the inside with a piece of transparent tape to contain the resin. Take care not to touch the halogen bulb itself because your own skin lubricant on the glass could carbonise under heat and cause the lamp to explode. Remember that you are repairing a real lens that concentrates and directs the light of the bulb. The resin you add will not act as a lens, so avoid any buildup of resin directly in front of the bulb that could distort light from it. Red or orange tail lamps also can be repaired with clear Liquiglas resin.