I had the same trouble actually. We couldn't figure out why my instrument panel lights weren't working. Everytime we'd replace the fuse it would go out again. It turned out someone who owned the car before me had tried to ground the radio to the instrument panel wire. We found that out after we bough a new switch and everything. Bah, good luck, also the panel lights don't show up at all until night time.

 

Mine don't work either. The headlights work, but the dash is dark. Maybe I'll go to Ford and see if it's still under warranty...

 

Take the switch out to check to see if the wire going to the panel has come off. Also check to see if the panel is grounded. For a wiring diagram, google it. Just type in 1967 Mustang wiring diagram, and you will get some diagrams for you to see if your's is hooked up right.