A Winthrop volunteer auxiliary police officer accused of selling cocaine pleaded not guilty Thursday to federal drug charges. Bledar Naco, 34, entered his plea in federal court in Boston, court records show. The complaint alleges that he sold cocaine in his Mercedes vehicle to an undercover police officer in October. Winthrop police have said the investigation started after they received tips that Naco allegedly dealt drugs out of his police cruiser while in uniform on several occasions. Naco is free on bond.Travis Andersen can be reached at email@example.com.