wire constant through a relay and take the foglight switch wires and run fused power in on one side and run the other side to activate relay and youa re done. Its pretty simple. Mine are wired that way. you shoudl put them on a relay even if you maintain the stock wiring to the switch sense there has been a known tech bulletin for the switch failing/heating up. (some one will correct me on exact problem)
SEE http://www.corral.net/tech/maintenance/foglights.html to fix the problem. The stock wiring isn't up to the job and is overheating. The headlight switch & turn/multifunction switch are affected by Ford's wiring problem. Sometimes it overheats so badly that the plastic shells of the wiring connectors start to melt. This will show you how to add a relay to the fog lights to relieve the overload on the headlight wiring.