Hey, no one could answer the problem better than me. If it's a GT and foglights are on it's the factory Ford light relay because your over heating the headlight relay which causes headlights to flicker.
Second, if it's and LX than it's the actual headlight switch. I drove for 2 months pulling it out hold out the window cool off then plug back in NO JOKE. All you have to do is pull out a bit then look in and there is a clip, just stick a screw driver in and pry outward. Very easy, and don't piss around with old ones, or just cooling it off, I've done both a new one cost me $40.00CDN after 15%TAX so it's not worth the hassle. I do grab spare ones whenever I can though, you never know eh.
