Staying safe while trailering your boat means making sure your boat trailer lights are working, your boat trailer wiring is not cut or sliced, and your connectors are clean and making a solid contact.
Boat trailer wiring is simple, two wire: one positive and one negative running from a 12 volt battery to the light. Coming from your tow vehicle will be more than 2 wires however. Realize that this wiring harness will have to accommodate signals from your tow vehicle for: tail lights, braking, left turn signal and right turn signal and a wire for the negative terminal. The focus on this page will be maintaining your boat trailer lights in working order.
Boat trailer tail lights are manufactured to be waterproof since they are immersed in water each time you launch your boat. Recently these tail lights have become available with LED lights. LED's are somewhat brighter, and promise a much longer life. Although more expensive they can be a great value since they will outlast conventional bulb tail lights. It is a good idea to carry with you a replacement tail light unit for both the right and left side of your trailer. These two units are not interchangeable so I carry one of each because my experience has been that I have never discovered a burned out light while parked in front of an auto part store.
Also suggested is to carry along an electrical kit containing wire stripper/cutters, electrical tape, dielectric grease, and a variety of wire connectors. Most minor electrical repairs can be handled with this kit. These connections are easy for do-it-your-selfers. In addition, auto parts stores are a great resource for parts and advice.
See and be seen. This SeaChoice LED submersible light bar for the lower rear of your trailer will light up your back side for a long way. LED means it will last longer than traditional lamps and will add to your overall safety. Easily change and replace an existing bar that is broken or burned out. Check it out.
Boat trailer lights made for clearance (for example outside edges of fenders) are added to trailers as a safety precaution. They are placed on portions of the trailer that mark the outermost parts of the trailer, so that at night others are able to see and avoid hitting the trailer. They are also helpful for the driver when backing the trailer after dark. Replace any boat trailer lights that have burned out on your trailer including clearance lights. These are often a simple snap in unit. Adding a bit of dielectric grease onto the fasteners will help maintain a dry and clean connection. Keep 1-2 spares as these clearance lights can also be damaged from road debris.
Most anglers want their boats and trailers to be easily seen at night by other drivers. Depending on how large your trailer is you may find that added safety reflectors or reflective tape may be helpful. These are available as self adhesive and are easy to install on any cleaned portion of your trailer. This need not be overdone, but should not be overlooked either.