Understand 4-Pin Round Trailer Wiring Diagrams

1 min read

Trailer Wiring Socket for a 4Pole Round Trailer

If you’re looking to tow a trailer with a four-pin round connector, understanding the wiring diagram is essential. Many trailers have four-pin round connectors, so it’s important to know the purpose of each pin and how to properly connect the trailer wiring.

Pin Functions

The four-pin round connector typically includes four separate circuits. The first is the ground or earth wire, and it’s typically the largest pin. The second is the left-hand turn and brake signal, the third is the right-hand turn and brake signal, and the fourth is the running lights or tail lights. The ground wire should be connected first and foremost, followed by the turn and brake signal wires, and then the running lights.

Connecting the Wires

To connect the wiring, it’s important to follow the instructions included with the trailer. If there are no instructions included, then it’s best to start with the ground wire. Once it’s securely connected to the connector, the other wires should be connected in the same order as they’re listed above. It’s important to make sure that all the connections are secure and that the connector is firmly attached to the trailer.

Installing the Wiring

Once all the wires are connected, the wiring needs to be installed on the trailer. The wiring should be routed away from any sharp edges and should be secured with zip ties or other fasteners. If the wiring is too long, it can be trimmed to the correct length. It’s also important to make sure that the wiring is not exposed to any corrosive elements, such as water or salt.

Testing the Wiring

Once the wiring is installed, it’s important to test the connection. This can be done by connecting the trailer to a vehicle and testing the lights. If the lights are not working, it’s important to check all the connections and make sure that all of the wires are securely connected. If the connections are all good, then it’s likely that the wiring is faulty and needs to be replaced.


Understanding a four-pin round trailer wiring diagram is essential for anyone looking to tow a trailer with a four-pin round connector. It’s important to understand the purpose of each pin and how to properly connect the wiring. Following the instructions included with the trailer, securely connecting each wire and routing the wiring away from sharp edges will help ensure that the trailer is properly connected and the lights are working.