I have actually had this happen to me twice. The first time it melted the harness that connects to the actual light switch. No big deal there, replace the harness and put it back together. The second time was weird, the harness melted but when I replaced it the problem was still there (lights flickering, not staying on etc..), what it wound up being was the multi-function switch (the thing with your hazard switch and turn signals). I think it cost me like $50, not too bad to replace, just have to take the steering collum apart. The guy at ford I was dealing with said that ford made some improvements on the original design to stop the melting from occuring. This was all a few years ago and I havent had it happen since.