I had the opposite problem with my 2012. I had the gray wire and wired relay spot but no wiring outside of the cabin to support the fog lights. After looking around for a good while i decided the easiest solution was to just run new wiring. I have it wired so that the switch only gets power when my headlamps are on, at which time it illuminates and i can turn my fog lights on or off. My wiring harness was quite simple, one wire supplies power to the switch, which when pressed then supplies power to close a relay, which supplies power from the battery to the fog lamps. Closest to oem i could get it without going to crazy with wiring. I also had limited wiring schematics to work with plus the wiring seems to differ over the years.