How to Troubleshoot Seven-Pin Trailer Wiring

by Bob White

Trailers come in many different sizes and functions to suit your particular need. Because trailers may sit idle for many months, however, it is common to encounter electrical problems when firing them up after a break. The harsh environment they are exposed to slowly corrodes the connections, creating problems. A seven pin electrical system is responsible for powering signals, markers, breaks, batteries and back up lights. Troubleshooting a specific problem is a process of trial and error.

Attach the trailer electrical connection to a tow vehicle with a dependable power source and run through all of the possible systems while recording the errors. You will have to use the 12 volt electrical tester on the connections to the battery to see if the vehicle is delivering power to it. Disconnect the battery before checking the connection.

Check the ground connection to the trailer frame for corrosion if there is zero power at the trailer. This is the most common problem with trailer wiring. The ground connection is the white wire at the harness. Repair as necessary.

Check the power supply with the 12 volt tester at any device which does not have electricity, if the problem is confined to just one or a few areas.

Work your way back through each connection on the wire with the 12 volt tester until you discover a live wire. This is where the connection problem is for this device. Make repairs to the connection.


  • check If you work your way all through the connection and there is still no power, it is possible the wiring harnesses itself needs to be checked.

Items you will need

About the Author

Bob White began his writing career in 2006. Working in sales, he was a technical writer tasked with responding to requests for proposal. White has a Bachelor of Arts in computer science and a diploma in home inspection. He has also worked in construction, landscaping and the pool industry for more than 15 years.

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  • photo_camera camping,trailer image by Greg Pickens from