True fog lights (not driving lights) should be mounted low, i.e. under the bumper. Make sure you wire them through a relay, and use 12 gauge wire to feed the lights. The switch lead to the relay can be much lighter wire, like 18 or so. Ground the lights using 12 ga wire as well, and pick a good spot for grounding. I use one of the horn mounting bolts, after scraping down to bright metal. Some folks wire the relay so that the fogs go out when high beams are selected, but I prefer to control them independently, so I use the parking light circuit to feed the relay.