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How to reliably wire a trailer

How to reliably wire a trailer

Metallic corrosion is the enemy of trailer electrical systems. Dirt, salt, water and road vibrations can loosen or damage electrical connections, resulting in trailer lights not working properly. Metal oxides such as rust are often insulators, meaning they do not conduct electricity well. Corroding metals often expand in volume, leading to additional mechanical stresses on electrical contacts.

Even zinc, copper, and aluminum can corrode in the right environments. A combination of dissimilar metals and salt water can be exceedingly prone to corrosion. Salts are common on all road surfaces and its presence is not dependent upon use of chemical deicing agents or a nearby ocean.

Wire Connections

A trailer cannot wire be wired without making electrical connections between two or more wires. If these connections are made with automotive splice connectors, the familiar blue, red and yellow plastic snap-shut products, they make good connections, at least initially. However, these connector are not designed to be water proof, and water, salt, and other corrosion inducing materials will attack these connectors. Eventually the steel connectors will stop making a reliable connection.

Water resistant connectors are available, and while they are more expensive, will result in less maintenance and repairs. Motorcycles are used in similar conditions to trailers, and connectors designed for motorcycles perform reliably in wet and corrosive environments. Motorcycle parts suppliers are found in most cities or online.

Rubbing Wires the Wrong Way

Copper wiring is run underneath the trailer, and usually through holes drilled through metal members of the chassis. These are prime spots for electrical failure, as the constant vibration and motion of the trailer causes the insulation to wear against the metal of the trailer chassis. A short circuit results, and a fuse will blow in the towing vehicle.

Short circuits are prevented by protecting the wiring from rubbing against metal. Rubber grommets can be fit into the drilled holes to protect the wiring. Wiring secured with metal hangers cannot vibrate or move with trailer motion.

Sacrificial Trailer Connectors

The plug where the trailer attaches to a vehicle’s electrical system will receive wear and tear in normal trailer use, creating a need for repair and maintenance. A sacrificial connector can mitigate this problem.

A sacrificial connector is a small wire bundle with connectors at both ends. One end plugs into the trailer, and the other end into the vehicle. This wire and connector takes all of the wear and tear, and can be easily replaced without any rewiring. Short, pre-assembled cables are available in a variety of connector types, and work well for this purpose.

The Ground Wire

Nothing causes more electrical problems on a trailer than the grounds. Utility trailers typically make a ground electrical connection to the towing vehicle through the ball hitch, and this is usually reliable because of the constant wiping action within the hitch during towing removes any corrosion.

The problem usually occurs in the connections for individual lights to the chassis ground. These connections are often made by wrapping a wire around a screw which is inserted into the chassis Exposed connections are prime candidates for failure due to corrosion and vibration.

The solution is to make one very secure ground connection between the chassis and a ground wire. This connection should be made with a nut and bolt, with the wire anchored securely to bare chassis metal.. Coating the whole screw and exposed wire with a metal gripping epoxy will eliminate the risk of corrosion or loosening of the screw. This ground wire can them be routed to all the lights along with the other wires.

Wiring Standards

There are common standards for wire color used for trailers. While a trailer could be wired with every wire the same color, maintenance becomes much harder. Different wire colors allow quick and easy identification of individual wires. The use of standard colors allows other individuals to provide assistance in diagnosis and troubleshooting.

Pre-assembled wiring harnesses are available from most trailer supply sources, and assure wiring conformance to standards.

Trouble Free Trailer Use is Possible

Careful selection of components and following the outlined procedures can reduce the number of trailer wiring problems. A utility trailer is a very unforgiving environment for electrical and metal components, but with minimal effort common problems can be eliminated.