Hi Neoboy,
There should be a relay that supplies 12v at high current to the headlights when the headlamp switch is on (in the engine compartment). (High current does not flow through the headlight switch on the steering column). You should connect your fog lamp hot lead switch to this relay terminal. Then, make sure that you have solid ground connections from EACH fog lamp to the car's chassis using 12 or 14 ga wire. The ground connection is critical because you may be getting unwanted current/ground loops through other circuits. Also, make sure the headlamp relay can withstand the extra current flow from the fog lamps or it will fail prematurely. If they are 50 watt lamps, the added current will be about 8-10 amps at 12v. (Best) You may want to add another relay (in the engine compartment) that is controlled by the fog lamp switch to actuate the fog lamps. It's not a good idea to have high current flowing through a small switch inside the passenger cabin. Could cause a fire. I can e-mail you a simple schematic if you like.