Troubleshooting Trailer Lights that do Not Work Using a 7-Way to 4-Way Adapter

Updated 06/12/2017 | Published 06/09/2017

Question:

We have no trailer lights, but when we turn on a turn signal, both lights on the back of the trailer start blinking. On the other hand, when we turn on the 4 way lights in the vehicle, we get nothing. We use a 7 prong to 4 prong adapter, and everything seems to be hooked up correctly. Everything on the vehicle seems to work, too. Is there something we missed or did incorrectly?

asked by: Travis

Expert Reply:

Start by using a circuit tester like # PTW2993 to test the functions on the 7-way connector at the back of the vehicle. If all checks out, do the same with the 4-way adapter plugged in. If you know there's a problem, it's the adapter. If there's still no problems here, then you know the issue is on the trailer. If you had a problem at the 7-way when you first tested it then you know the issue on the vehicle. Also, make sure each connector, vehicle, adapter, and trailer are clean and free of any corrosion.

Once you know whether the problem is on the vehicle or the trailer, you'll want to check the ground connections and make sure they're grounded to a clean, bare metal surface. If the lights are grounded through the mounting hardware, make sure the studs are clean too. Then inspect the wiring for any pinch points or damage.

If you still can't narrow down the problem let me know what you have found and we'll keep troubleshooting. I've also linked an article on trailer wiring you might find helpful.

expert reply by: Charles S