It wouldn't be likely that fuses are causing the flickering. They are either blown or not.
Replacing the switch is a good start. If the problem persists, it could also be the turn signal switch. Ford made these really bad and if you ever opened it you'd see carbon deposits from major arcing. Over time it will eventually fail completely. To test this theory, you may want to try jiggling the turn signal switch and see if your lights flicker as you jiggle.
I've had this happen to me twice over the 155K life of my car. The first time I just opened the switch and cleaned it up. The second time I just replaced it. I can't remember if the foglights would go on but not the headlights, but I think that is what happened since when I was driving there was some light coming from the front.
Oh, to remove the headlight switch, all you have to do is depress the tabs on the switch on either side and it should just slide out. You probably can do one side of the switch at a time. Use a small flathead screwdriver.
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351W 89 Mustang GT Convertible