Introduction
Trailer connectors are crucial for the safe operation of semi trailer trucks. These connectors, when used with trailer cables, serve to connect the tractor to the trailer’s lighting and signal control systems. Some commercial trailers also incorporate ABS control and power supply functions. Additionally, certain cargo trailer connectors are designed for power supply functions related to truck tail lift control. Among all trailer connectors, the 7-pin type is the most common.
However, are all 7-pin trailer connectors the same?
The answer, of course, is no.
What is a 7-pin trailer connector?
7-pin, 7-way, 7-wire, 7-core—anything related to trailer electrical connections seems to be associated with the number “7.”
Why not 3 or 5? This is determined by the number of lights on the trailer.
Common trailer lights include:
Left turn signals
Right turn signals
Rear fog lights
Right-side marker lights
Left-side marker lights
Brake lights
Including the ground wire, there are a total of 7 wires. Clearly, missing any one of these pins would be a significant headache for trailer modification workshops.
Please check the blog if you want to learn more about the trailer wiring.
The primary reason for not using 13–15 pin trailer connectors is economic. While a 13-pin trailer plug may not increase costs significantly, it not only raises the price of the plug but also of the cable. A 15-core cable is expensive.
The following image shows several common 7-pin trailer connectors. Clearly, they are all different, with variations in pin arrangement and materials.
Different types of 7-pin trailer connectors
Here, I would like to explain from two perspectives why not all 7-pin trailer connectors are the same:
National/regional standards
Materials
1. 7-pin trailer connectors with different national/regional standards
(📌 Focus: Pin arrangement differences)
Common standards:
United States: SAE J560 and SAE J2863
SAE J560 Wiring Europe: ISO 1724 12N and ISO 1185 24N
ISO 1724 Wiring Australia: AS 2513 and AS 4735
👉 A common question:
Can I use a standard trailer connection cable to connect a trailer with an AS 4735 socket to a tow vehicle with an ISO 1724 standard?
Answer: No.
Example:
The 5th pin of the Australian standard AS 4735 is for electronic brakes
The ISO 1724 standard uses it for position lights
➡️ If the position lights are turned on, the trailer will brake.
Solutions:
Replace the trailer socket at one end and rewire it
Select a trailer conversion connector cable
2. 7-pin trailer connectors made of different materials
Besides pin arrangement, materials also differ.
Housing material: plastic, metal
Pin material: nickel-plated, gold-plated
🔎 Metal housing + gold-plated pins = more expensive but more durable.
Plastic quality also varies—cheap plastic is weaker, while reinforced plastic is much stronger.
This explains why some sellers offer trailer connectors for $1 with free shipping, while others charge $2 at EXW price.
👉 Quick tip: The simplest way to distinguish quality is by weighing the connector. Heavier connectors may indicate better quality. (Reference only; not the sole criterion)
FAQ
How do you test a trailer connector?
-There are trailer connector testing instruments available, and they are not expensive—costing around 2–3 USD.
How to wire my 7 pin trailer plug?
-Please check this article
Do trailer lights need to be grounded?
-Yes. There is one pin for ground on connector.
What is the color code for 7 wire trailer lights?
-White Black Yellow Red Green Brown Blue
Conclusion
Not all 7-pin trailer connectors are the same.
When using them, ensure your trailer meets the correct standards and is fully compatible. If the truck and trailer have different standards, a converter may be needed.
A converter adapter can be either a connector or a cable.
KMCABLE is familiar with trailer connector standards in various countries. If you wish to customize a converter cable, especially a trailer spiral adapter cable, please contact us at any time. We will provide the most professional service and products.
