Anyone who has launched a boat via a trailer soon realizes that the lights on the trailer function correctly right up to the first submersion. After that, it’s anyone’s guess. The left turn signal will function, but not the left brake light; only the brake lights work, but not the signals; signals work at random and the running lights have disappeared.
Each spring brings a trip to the auto store to buy new trailer lights. The hermetically sealed package clearly states that the lights are “submersible.” Indeed they are; they go underwater quite well. What the packaging does not state is that the lights will never work correctly after being submerged.
Therefore, I suggest that all boat trailer owners purchase magnetic trailer lights. These lights are used when towing cars and come with a 20-foot extension. They work just as well on boat trailers. When you arrive at the marina, pull the lights off the trailer and stow them in your car. They never enter the water.
The magnetic tow-light kit may be a bit pricey, around $80, but if you plan on owning your boat trailer for a while, it would be a good investment.