I wired a set of Hella Micro DE fog lights in the factory location using the factory wiring and it lasted roughly a year and a half before I had issues. The factory wiring seems to get brittle. I found several spots where the plastic coating around the wire has flaked off.
I would recommend using a heavier gauge wire so you don't have to re-wire a year or two down the road.
I'm currently putting off re-wiring my fog lights after several days of trouble shooting those damn lights.