Premier Manufacturer
Custom trailer wire harnesses are designed to deliver stable power and signal transmission between towing vehicles and trailers.
Romtronic designs and manufactures application-specific trailer wire harnesses for utility trailers, RVs, agricultural equipment, semi-trailers, and heavy-duty transport systems.
Our trailer harnesses are engineered to withstand harsh outdoor environments, including moisture, vibration, dust, and temperature variation. From standard 4-pin systems to complex multi-function harness assemblies, we support both prototype development and scalable production.
Our Custom Trailer Wiring Harness Styles
Below are examples of custom trailer wiring harnesses we manufacture. If you require additional references, regional configurations, or application-specific samples, our engineering team can provide further support.
Why choose us for custom trailer wiring harnesses?
Choosing Romtronic for your custom trailer wiring harness means getting a product designed to handle extreme weather conditions. Whether your trucks operate in icy, slushy environments or scorching, dusty terrains, our harnesses are designed to ensure your equipment stays running smoothly. Our advanced braiding technology provides reliable control over every part of the electrical system, from lighting to braking. Additionally, our custom potting materials enhance durability, reducing replacement costs.
With our cutting-edge ERP system and detailed production documentation, Romtronic guarantees consistent, high-quality results. We’re proud to hold certifications such as ISO 9001:2015, ISO 14001:2015, ISO 45001:2018, and IATF 16949, ensuring adherence to top-tier standards. And with 24-hour online service, we’re ready to respond quickly to your inquiries, from drawings to orders.
Our Quality
At Romtronic, we produce high-quality custom trailer wiring harnesses. The technical quality of each cable component is verified through stringent electrical testing conducted by IPC/WHMA-A-620 standards (our quality control procedures are outlined in a separate document) and ISO requirements. We can assist you with ODM and OEM wiring harness orders, thanks to our multiple quality certifications and over 20 industry patents. Please let us know if you would like to receive our quality manual now.
Trailer Wire Harness Manufacturing Process
Our trailer harness programs follow a controlled production workflow to ensure consistency and electrical stability.
Design & Engineering Review
Review of electrical functions, pin definitions, routing conditions, and environmental requirements.
Prototyping & Sample Validation
Prototype harnesses are produced to verify fit, connection logic, and performance before production.
Wire Processing & Sub-Assembly
Cutting, stripping, labeling, pre-assembly, and installation of protective tubing and sealing components.
Terminal Crimping & Mechanical Assembly
Automotive-grade crimping and mechanical assembly to ensure secure electrical connections.
Final Assembly & Electrical Testing
Harnesses are assembled to layout boards and electrically tested for continuity, shorts, and insulation integrity.
Common Trailer Wiring Harness Specifications and Applications
Trailer wiring harnesses can have various configurations based on the number of pins. Each pin serves a distinct purpose and connects the trailer’s electrical system to the trailer itself. Standard trailer wiring harnesses come in 4-pin, 7-pin, and extended versions—the big jump is to 13-pin.
1, 4-Pin Trailer Wire Harness: This is the most basic and commonly used trailer wiring harness. It provides essential electrical connections for the trailer’s brake lights, turn signals, and tail lights. 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, 77-Pin Trailer Wire Harness: Adds extra connectors and is standard on larger trailers and agons. 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: This 13-pin trailer harness is commonly used in Europe and other regions. It retains all the wiring harnesses of the 7-pin trailer wire harness but adds a few more. The 13-pin harness connections are as follows:
- Pins 1-8: Same as the 7-pin harness (ground, tail/marker lights, turn/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, driving lights, refrigerator power, or trailer stability control.
It is worth noting that the function of each pin can vary depending on the wiring specifications used in your region. Please refer to your vehicle manual or wiring diagram before installing and connecting your trailer.
Frequently Asked Questions (FAQs)
Q1: What types of trailer wire harnesses do you manufacture?
We offer a wide range of trailer wire harnesses, including 4-pin, 5-pin, 6-pin, and 7-pin configurations for utility trailers, boat trailers, RVs, and agricultural equipment. Custom designs are also available based on your specific vehicle or application.
Q2: Can you customize trailer wire harnesses for different regions or standards?
Yes, we can manufacture wire harnesses that meet North American, European, or other regional electrical standards. Just share your specs or drawings, and we’ll deliver a compliant solution.
Q3: What materials do you use to ensure durability and weather resistance?
We use high-quality automotive-grade wires, PVC or TPE jackets, and waterproof connectors to ensure excellent resistance to abrasion, moisture, and extreme temperatures—ideal for outdoor and off-road environments.
Q4: Do you offer sample or prototype wire harnesses?
Absolutely. We can provide samples or prototypes for evaluation before moving into mass production. This ensures the final product meets your design and performance expectations.
Q5: What is your typical lead time for trailer harness production?
Lead times vary depending on order volume and complexity, but standard orders usually ship within 2–3 weeks. We also offer expedited options if needed.
Get in Touch for Custom Trailer Wire Harness Solutions
Romtronic provides high-quality, custom trailer wire harnesses tailored to meet the specific needs of utility trailers, boat trailers, RVs, agricultural trailers, and more. Whether you require 4-pin, 7-pin, waterproof, or multi-function trailer wiring, we have the experience and capability to deliver reliable solutions.
To request a quote, discuss your project, or get expert support, feel free to contact us through the form on this page or using the details below — our team will respond within 12 hours.
📧 Email: info@romtronic.com
📞 Phone: (+86) 199-2816-5824
Romtronic is your trusted partner for custom trailer wiring solutions, serving customers in over 80 countries worldwide.