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Hello and welcome to just answer and allowing me to assist you. Is this a new trailer wiring or have you had it for a while Is the trailer new to the car wiring ?Most asian and or European vehicles have an adapter modual for the trailer wiring to seperate the signal brake and tail lights from feed back .I suspect if the wiring has worhed before and not now that that uint is faulting out and needs replacing.But before you do you can check all connections and grounds for the trailer wiring. make sure every thing is tight and no corrosion.