From what I've read, I gather the Edge (along with many, if not all new Fords) has/have a lighting control module to take care of flashing. This may not work for the Edge and newer Fords then, but for the flasher to work, it needs enough electronic resistance to trigger the flasher. At the flasher, there is Power and Load (also, sometimes ground). If you connect one end of a resistor to the Load and the other to Ground, there'll be no need for a resistor in any exterior lights. Whether turning left or right, the resistor will allow the flasher to flash normally and will operate left and right correctly.