Dot Trailer Light Regulations


If you’ve ever had to travel with more than you can carry in your car or truck, then you’re most likely familiar with the seemingly simple frustration of trailer lights. The concept is simple: a trailer should have signals in the rear similar to a car so that those behind can see you braking and signaling a turn. In practice, however, you are fighting everything from mother nature to incorrect installation and wear and tear. Eventually, if not monitored regularly, it will result in a light failure and a potential traffic ticket.

Legal Requirements for Trailers: Two Categories

The need for trailer lights when traveling on public roads isn’t just required out of courtesy to others. It is required by state and federal road laws. How that law applies depends primarily on the size and length of your trailer. Two categories exist based on trailers under a width of 80 inches and those that exceed that number. New trailers are already manufactured with these requirements in mind, but some smaller kits that are pre-fabrication packages may require installation.

Legal Requirements: Physical Installation

The location of lights is defined in law as well. Generally speaking, all of the lamps and lights involved need to be attached in a permanent manner to the trailer and then also have to be consistent with the lighting and reflection requirements specified by the government. In fact, the lights’ housings cannot be just installed in any old manner. They have to line up with a 180 degree and a 90 degree angle specification detailed in statute. The only exceptions are those that are blessed in design by the government to work at an angle. Further, the parts of the trailer or vehicle are not allowed to restrict or block the signals from working or being seen visually by other drivers. Again, only specified exceptions are allowed, usually involving some kind of extension that allows the light to be seen above or further out from the trailer or vehicle part.

Wear and Tear

Due to the fact that many trailer lights, whether they come from a trailer manufacturer or aftermarket add-ons, are exposed, they are prone to being damaged. The problem is the installation design. More often than not, the wiring for the lights comes from underneath the trailer. Road grit and stones bounce up constantly from the road, and wind friction pushes at anything loose. Eventually, an errant rock or tugging from wind will wear down an open spot in unprotected wiring insulation. Then you begin to have intermittent shorts in the signal. Ultimately, the wire will completely short or severe, and the light won’t work at all. The answer seems simple: check the wires regularly. But this is easier to say than do. People wire up trailers and forget about them until a problem occurs.

Boat Trailer Problems in Particular

Trailer lights used for boating transportation are the most prone to damage. Not only do they get the wear and tear of the road, but they also get exposure to water and lots of backing up on boat ramps. That usually means more likelihood of minor collisions with the boat dock. Water exposure is the easiest culprit, but also the most preventable. A hot bulb will explode when put in contact with cold water. But unplugging the lights prior to backing up the trailer will avoid the problem and potential delay on the way home later on.

Final Note

Always remember, whatever trailer or trip you take with one, to bring extra bulbs and a spare trailer wheel with you as a precaution. Most folks fail to think about this because failures are few and far between. However, they do occur, and you don't want something as simple as a blown trailer light to put a downer on your trip with a traffic ticket.

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