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Troubleshooting Dealer-Installed Wiring Harness on 2017 Jeep Wrangler


I have a 2017 Jeep Wrangler with a Mopar tow wiring harness which was installed at the dealer. I am towing this vehicle behind a 2011 Sprinter chassis motorhome. The lights do not work on the Jeep when hooked to the motorhome. I have power to the Jeep checked harness with test light and when turn signal is on in Sprinter, I do hear the relay clicking, but again no lights. To verify that the Jeep lights are working, I hooked it to my wifes 2014 Dodge Ram, and all lights, brake, and turn signal does work on the Jeep. I am leaning towards a bad ground on the Sprinter, but maybe you have heard something with this combination of vehicles. Thanks in advance.


Expert Reply:

The types of wiring harnesses used for flat towing a vehicle behind a motorhome and for towing a trailer with the vehicle are different. If the dealer installed a standard trailer towing wiring harness this will not function correctly for flat towing the Wrangler behind the Sprinter. For reference I linked our main pages for both types of wiring kits for your 2017 Jeep Wrangler.

But if the dealer installed a flat-towing type harness such as Hopkins # HM56200 it should make no difference what vehicle is feeding signals to the harness. We know of no specific compatibility issues between Sprinter and Jeep vehicles.

I suggest you apply a circuit tester like # 40376 to the Sprinter's connector to confirm the signals are making it all the way there. Use of the tester is shown in the linked video. Hearing the blinker relay is a good sign but does not guarantee that its output is making it to the Sprinter's trailer connector. The linked article will help you with the testing process.

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