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Custom Trailer Wire Harness

Custom Trailer Wire Harness

To connect the electrical system between a trailer and a tow vehicle, you need a wiring harness known as a Trailer Wiring Harness. These include the wires to carry power and signals with connectors (often, both mating connections on a single cord), which plug into corresponding links and must be electrically the right way around.

Benefits of a trailer harness:

  1. Easy assembly: The trailer wiring harness uses a standardized design, which makes it easy to connect the trailer wiring harness with your vehicle’s factory original wiring and no complicated setup or tuning is required.
  2. Applicable to many types of vehicles: Trailer wiring harnesses are applicable for cars, station wagons, trucks (trucks), boat trailers, and other series.
  3. Weather resistance: A trailer wiring harness is crafted using high-quality materials that are built to last and can indeed stand up to wintery environments as well.
  4. Multi-functional design: The trailer wiring harness adopts a multi-functional design, and different electrical equipment of a vehicle will be required to connect for different purposes like lights, brake systems signal transmission, etc., which requires the full range of electric support.
  5. High-performance power supply: Trailer wiring harnesses are designed to offer a consistent high-power power output that ensures the proper functioning of any connected accessories.
  6. Plug and play: Easy To Set Up And RemoveTrailer wiring harnesses have a design that utilizes a plug-and-play interface and the most important feature of this setup is it allows you to quickly connect or disconnect your light bulbs without having standard painful electrical connections.

We Offer Custom Trailer Wiring Harness Services

Romtronic is a customer-focused manufacturer of custom wiring harnesses and custom cable assemblies. One of the main products is trailer wiring harnesses. By working directly with a customer through our team of professionals and years’ worth of experience, we can facilitate an understanding to take their requirements from concept to full-on wiring harness solution.

We achieved the quality system certification ISO9001:2015, 14001:2015, 45001; TS16949 (Automotive), UL/CE/MFI certificate, and passed the full test for USB4-TID-91105. Our wiring harnesses are of high quality, using only top materials and components that meet strict standards. Moreover, our harnesses are rigorously tested for durability and reliability.

24-hour online service, within 12 hours reply to your inquiries about drawings, samples, orders, and engineering issues.

Our Custom Trailer Wiring Harness Styles

The following are some of the personalized items we produce, trailer wiring harness products. If you would like to see more pictures of our products, congratulations on your prompt response.

Common Trailer Wiring Harness Specifications and Applications


Depending on the number of pins, a variety of configurations are possible with trailer wiring harnesses. The purpose of each pin is different and it connects the trailer electrical system to the trailer. Standard trailer wiring harnesses are 4-pin, 7-pin, and the extended version – a massive leap to 13-pins.

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: -Adds extra connectors and is common on larger trailers/wagons. The 7-pin harness provides the same features as the 4-pin harness with these additions:

  • 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: 13-PIN Trailer Wire Harness: This harness is generally used in Europe and other possible regions. Of all the 7-pin harnesses, it retains all but adds several more. The 13-pin harness connections are as follows:

  • 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.

Please note the functions of each pin can be different based on which wiring specification is used depending on the region. Always refer to your vehicle’s manual or wiring diagram before attempting installation and, before connecting a trailer.