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Only Running Lights on Trailer Work After Installing Hopkins Wiring Harness on 2007 Mercury Mariner


After installing part #40455 and hooking up my trailer, the only lights that work are the lights that come on at night/when my headlights are on. Brake lights and turn signals dont work. Do you think I just got a faulty part?


Expert Reply:

Vehicles using trailer wiring harness # 40455 may need to see a local Ford or Mazda dealer for a relay. The relay is needed to activate the tow package wiring circuit. It sounds like your 2007 Mercury Mariner is missing that relay. Also check to make sure that the trailer side connector is clean and free of corrosion because that can cause lights to not work.

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