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Trailer Lights Malfunction on a Small Utility Trailer Behind a 2009 GMC Acadia with Factory 7-Way  


I have a factory installed towing package which includes a 7 blade plug receptacle. I just purchased a small utility trailer with a 7 blade plug wired to it. I have running lights but no brake or turn signals. I have been trying to diagnose the problem for hours with no luck. I have double checked the wires and connections and cleaned & reattached the ground to the trailer. Still no luck. I see on your site that there should be no issues with vehicle LED vs standard bulbs on the trailer. Help! Can you give me anyn suggestions. Thanks.


Expert Reply:

Vehicles with LEDs will have problems with standard trailers unless a powered tail light harness is used, or there is a factory tow package. If your 7-Way on your Acadia is indeed a factory connector, you should have no problems with LEDs vs. incandescent lights.

Most small utility trailers do not have a 7-Way. 7-Ways are used on larger trailers that have electric brakes, or hydraulic systems powered by a battery, or boat trailers with hydraulic actuators with reverse lockouts.

If your trailer was previously owned it is possible that it is wired incorrectly. It is also possible that something shorted one of the tow circuits on the Acadia resulting in a blown fuse or relay that needs to be replaced. The first step is to isolate the problem between the trailer and the vehicle.

Use a circuit tester, like part # PTW2993, to check the 7-Way on the Acadia. If everything works properly, then the Acadia is not the problem. If it does not work, I would start checking fuses and relays on the power block in the engine bay. I have added a link to a wiring FAQ page that shows which pins should serve which function. Use the circuit tester to make sure everything is on the correct pins. If everything checks out, then your truck is probably fine, and the problem is on the trailer.

Again, take a look at wiring FAQ page and make sure the wires from the trailer are terminated at the proper pin on the connector.

Either one of these causes is just as probable as the other. It would be worth the time to do a quick fuse check in the engine bay. The cover should have a map or listing of all the fuses. Check all of the fuses that have anything to do with tail lights or tow circuits.

expert reply by:
Patrick B

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