that's correct. this additional wire will server to power the parking/side marker light.
the original 2 wires that are on Euro installs will be the flasher power source and the ground wire.
What would probably work best for you, if you've not already completed your install, is rather than change around the configuration of the side markers, leave them as they were originally (ie. North American setup) and just run the extra wire from the side marker power source to the city light. if you've already figured it out then it's a moot point.
