On most trailers, this means the lights are going under water. Take the time to disconnect or switch off your trailer lights just before you launch the boat. You can often make your trailer lights waterproof by caulking the taillight housing to prevent leaks. Even so, water often finds its way into the housing, and the prepared boater always carries a few hand tools and some spare trailer bulbs. The bane of every boater seems to be trailer lights.
Many designs are tender and touchy.
The prepared boater would rather fidget, fuss and fix his trailer lights in his garage in April than curse at them just before a big trip. Clean off the connections, check for wear and test that the turn signals, brakes and lights are all properly in sync between your tow vehicle and your trailer lights. Launching the boat often means backing the trailer into water that is deeper than the wheel hubs. The hubs get darn hot as wheel bearings whirl around the chase and allow the wheel to turn freely. Inspect, clean and grease cables to keep winches moving smoothly.