Lights arnt working right

I have a little bit of a not so serious big problum... My 91 5.0 Mustang has a problum with the lights shutting off while driving it... And at night this can become quite the hazard. But the lights only shut off if I am using the fogs... If I use just the main lamps I dont have a problum. Even when I have the highbeams on and the fogs on (but arnt working because the way it was set) they trip off. I dont seem to have a problum at all with them off. So if anyone could help me trouble shoot this that would be great.

check the light switch.. and the plug in for it for burned or discolored terminals,,,they overheat and mess up the switch..and alot of the time mess up the plug that connects to the light switch

Ok thanks. Il pull that apart and take a look in the day light