First, clean and wet both the overlay and the tail light. You can use a mixture of a drop of dishwasher soap and water. This will help you align the overlay properly. Place the overlay in the right spot and then use your fingers to squeegee out the water. This way, you won't damage the overlay's surface. Let the overlay sit for 24 hours so it fully sticks to the tail light. Once it's completely dry, it can withstand automatic car washes and most power washing. To keep them in good condition, just wash them gently with a mild soap and water when needed.