Show wiring diagram for fog lights

You can run a hot and ground from battery to a relay, and wire(s)to Fog lights, and 1 or 2 wires from relay to switch. Then you need a switch, Single Pole/Single Throw or a Momentary pushbutton switch if using a Latching Relay. Let me see if I can find the circuit for you.

Look through these circuits:
It can be done a couple of ways.
Relay Diagrams - Quick Reference (http://www.the12volt.com/relays/relaydiagrams.asp)

I installed a kit for a friend and I remember it was tied to the low beam circuit so high beam and fog can't be on simultaneously. May have been required in that state.

Sorry, forgot the link:
How To Wire Fog And Driving Lights Harness Wiring Diagram (http://www.accessconnect.com/fog_driving_lights_wiring.htm)