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Custom Trailer Wire Harness

Custom Trailer Wire Harness
Custom Trailer Wire Harness

A trailer wiring harness is a type of wiring harness that is specifically designed to connect the electrical system between the trailer and the tow vehicle. It consists of wires used to carry signals and power, as well as connectors and plugs used to link the electrical systems of the trailer and tow vehicle. Trailer harnesses have many advantages:

  1. Simple installation: The trailer wiring harness adopts a standardized design, which is relatively simple to connect with the original wiring harness of the vehicle and does not require complicated adjustments or modifications.
  2. Wide applicability: Trailer wiring harnesses can be applied to many types of vehicles, including cars, station wagons, trucks, boat trailers, etc., so they can be widely used in different scenarios.
  3. Weather resistance: Trailer wiring harnesses are usually made of high-quality materials with good weather resistance, able to work in various harsh environments, and not easily affected by external factors.
  4. Multi-functional design: Trailer wiring harnesses usually have a multi-functional design that can meet the needs of various electrical equipment connections, such as lighting, braking systems, signal transmission, etc., to provide a full range of electrical support.
  5. High-performance power supply: Trailer wiring harnesses usually provide stable and high-power power output to ensure the normal operation of the connected devices.
  6. Plug and play: Trailer wiring harnesses offer a plug-and-play interface design, making installation and removal quick and easy, without the need for cumbersome wiring connections.

We Offer Custom Trailer Wiring Harness Services

Romtronic is a manufacturer specializing in custom wiring harnesses and custom cable assemblies. Trailer wiring harnesses are one of the company’s key production items. With our professional team and abundant experience, we are capable of working closely with our customers to comprehend their needs and design a wiring harness solution that meets their requirements.

We have passed numerous quality system certifications, including ISO9001:2015, ISO14001:2015, ISO45001:2018, ISO13485:2016 (medical), IATF16949:2016 (automotive), USB4 TID:9115, UL certification, CE certification, MFi certification, and more. We adhere to strict quality requirements for our wiring harnesses, employing only high-quality materials and components. Additionally, our harnesses undergo rigorous testing to ensure their durability and reliability.

We provide 24/7 online service and can address your inquiries within 12 hours, including drawings, samples, orders, and any other engineering issues.

Our Custom Trailer Wiring Harness Styles

Here are some of the custom trailer wiring harness products we produce. If you would like to see more images of our products, please do not hesitate to contact us.

Common Trailer Wiring Harness Specifications and Applications


Trailer wiring harnesses come in different configurations depending on the number of pins. Each pin has a specific purpose and is used to connect the trailer’s electrical system to the trailer. The most common trailer wiring harnesses are 4-pin, 7-pin, and 13-pin connectors.

1, 4-Pin Trailer Wire Harness: This is the most basic and commonly used trailer harness. It provides the basic electrical connections for the trailer’s brake lights, turn signals, and taillights. The four pins correspond to the following functions:

  • Pin 1: Ground (connects to vehicle chassis)
  • Pin 2: Tail/marker light (rear light illumination)
  • Pin 3: Left turn signal/brake light (activates left turn signal and brake light)
  • Pin 4: Right turn signal/brake light (activates the right turn signal and brake light)

2, 7-PIN Trailer Wire Harness: This harness provides additional connections and is typically used on large trailers and wagons. In addition to the features provided by the 4-pin harness, the 7-pin harness adds the following features:

  • Pin 5: Electronic Brakes (sends a brake signal to the trailer’s electronic brakes)
  • Pin 6: Reverse Lights (activates the trailer’s reverse lights)
  • Pin 7: Auxiliary power (provides power to accessories such as interior lights, electric stabilizer, etc.)

3, 13-PIN Trailer Wire Harness: This harness is commonly used in Europe and other parts of the world. It has all of the features of the 7-pin harness but with additional features. The 13-pin harness includes the following connections:

  • Pins 1-8: same as 7-pin harness (ground, taillights/marker lights, turn signals/brake lights, e-brake, reverse lights, auxiliary power)
  • Pin 9: Reverse lights (another connection for reverse lights)
  • Pins 10-13: Other functions such as auxiliary power, running lights, refrigerator power, or trailer stability control.

It is important to note that the exact function of each pin may vary depending on the wiring standards used in different regions. It is always recommended to consult the vehicle manual or wiring diagram to ensure proper installation and compatibility with the trailer.