For those of us with hitch receivers a aftermarket brake light and wire it as a fog light.
http://www.etrailer.com/Hitch-Covers/Pilot-Automotive/CR-007XL.html
Or
http://www.etrailer.com/Hitch-Covers/Pilot-Automotive/CR-017.html
http://www.etrailer.com/Hitch-Covers/Pilot-Automotive/CR-007XL.html
Or
http://www.etrailer.com/Hitch-Covers/Pilot-Automotive/CR-017.html