See full version: How to Wire Trailer Lights — Wiring Instructions
Trailers longer than 15 feet and heavier than 1,500 lbs must have a brake system – that means another circuit for hydraulic brakes. The fifth wire (blue) is meant for reverse lights; this connection is needed to disconnect the hydraulic trailer coupler or actuator when the vehicle is backing up, thus deactivating the brakes on a trailer. more
Let’s see what types of connectors the trailer light wiring industry uses today. While the basic configuration is a 4-way flat connector that features one female and three male ends, you may come across connectors with up to seven pins for additional functions that require wiring, including electrically actuated brakes, power source for a winch, etc.
This is the most common scenario. It has three poles for basic functions (running lights, turn signals, and brake lights) and one pin for the ground. This connector is commonly found on most light-duty trailers. On the vehicle side, there will be a female connector, while the trailer/RV harness will have a male connector. When wiring trailer lights, make sure to route the harness away from anything that could damage the wires.
Before you tow any trailer, you should make sure it has functional trailer lights. Because installation works related to electricity scary many vehicle owners away, they prefer the experts at trailer shops to have the job done for them instead of trying to figure out how things work. However, in the simplest scenario on how to wire trailer lights, if you’ve bought a new vehicle, the only thing you will have to do is to find a factory-installed connector on it and get the right harness to attach it to the trailer.
Top of Rectangular Trailers more
There are two types of approved DOT reflective tape. Red and white striped tape, used for the back and bottom of the sides of trailers, must be two inches wide. The second type is white or silver reflective tape, used for the top of the truck's back end. While there are many types of reflective tape, the tape meeting DOT requirements must have “DOT C2” on the label.
Trailers that are rectangular must have red and white along the entire bottom of the back of the trailer and the entire lower rear bar as well. They also must have red and white on the bottom of both sides from front to back. This can be broken up into even segments, but tape must cover at least 50 percent of the total side length.
In December of 1992, the National Highway Traffic Safety Administration, which regulates the Department of Transportation (DOT), published a new federal law requiring reflective tape on all trailers and semi trucks that are at least 80 inches wide and weigh more than 10,000 pounds. The law is intended to cut down on accidents caused by poor visibility at night and in poor weather. The law also includes positioning requirements.
DOT C2 is a reflective tape that meets minimum reflective criteria in an alternating pattern of white and red. It must be 2” wide and it must be stamped with the DOT C2 marking. Two patterns are accepted, you may use the 6/6 (6″ red and 6″ white) or 7/11 (7″ white and 11″ red).
The rear of each trailer and semitrailer must be equipped with retro reflective sheeting (or reflex reflectors). Each strip of retro reflective sheeting (or reflex reflector) must be positioned as horizontally as practicable, extending across the full width of the trailer, beginning and ending as close to the extreme edges as practicable. The centerline for each of the strips of retro reflective sheeting (or each reflex reflector) must be between 375 mm (15 inches) and 1,525 mm (60 inches) above the road surface when measured with the trailer empty or unladen, or as close as practicable to this area. [links]
The 2″ DOT C2 retro reflective sheeting need to be applied to both sides of the trailer or semitrailer. Each strip of retro reflective sheeting must be positioned as horizontally as practicable, beginning and ending as close to the front and rear as practicable. The conspicuity treatment is not required to be continuous. However, the sum of the length of all of the segments must be at least half of the length of the trailer and the spaces between the segments of the strip must be distributed as evenly as practicable. The centerline for each strip of retroreflective sheeting (or reflex reflector) must be between 375 mm (15 inches) and 1,525 mm (60 inches) above the road surface when measured with the trailer empty or unladen, or as close as practicable to this area. If necessary to clear rivet heads or other similar obstructions, 50 mm (2 inches) wide retro reflective sheeting may be separated into two 25 mm (1 inch) wide strips of the same length and color, separated by a space of not more than 25 mm (1 inch). [links]
An evenly spaced pattern of strips 12”, 18” or 24” long may be used on each side of the trailer so long as at least 50% of each side is covered. more
There are several standards for trailer wires, and if you search, you’ll find a different Trailer Wiring Diagram for each. Each standard has it’s different purpose, so please don’t just make it up as you go. Don’t make a weird wired trailer. Follow these guidelines and make it right!
Lighter Duty Trailer (No Brakes) = Use a 4-Pin Connector.
The most common 4 wire connector is the 4-Pin Flat Connector as shown here. Trailers that use this are usually fairly light weight and don’t have brakes or other power accessories. It’s the most common style for “consumer” type trailers. Small utility trailers, light boat trailers, little campers, off-road trailers and many more use this traditional 4-Pin Flat connector.