Instrument lights non-op...

If you print out the wiring diagram from the link above, you can trace the dash lights back on the blue w/red stripe wire. It goes from the bulb back to the fuse block and goes through the small short fuse, then back to the headlight switch.
If the fuse is good, make sure it's making good contact. I've posted this problem before. I have found the connection where the wire is crimped to the terminal on the back of the fuse block to be corroded and rusted enough to disrupt the circuit. I've also found the fuse to LOOK ok, but one end is corroded and wll fall apart in you hands if you pull it out. Every restoration I now replace ALL the fuses. That has got me one too many times.
If you use a test probe, you can probe the fuse (wth the headlight switch pulled on) to see if you have power to one side or both. If you have good power (12 volts) on oth sides of the small fuse, check the headlight switch to make sure none of the connectors are extruding from the plug. THey should all be well below the surface of the plug. SOmetimes they will slip the catch ad work there way out of the plug. Ifyour good there, it's in th switch. When you pull the headlight switch on, it sends power into the coil, and the wiper picks up the power and sends it out to the fuse and out to the lights. The headlight switch "can" be taken apart and cleaned if you are meticulas and careful. The coil can anyway. But easily destroyed too. The switch is not overly expensive, but the coil may just need to be gently cleaned with an eraser. I've also seen (broken record for others here-sorry) the carbon bonded to the wiper fail. Pain to find. The bond holding the carbon to the wiper breaks down over time, Usually it falls off. But it can stop conducting. Seen it. Tested it a dozen times before I believed it. Then it fell off... That should be enough to make you dangerous...

Make sure you get the right ones. I had to have Carquest order 2/3's of the 5 fuses...and increadably, the easiest place to get that info is a owners manual. But can be figured out without it. If the fuse clips are rusted, you can ue a dremel and a small round abrasive stone to clean the rust off the inside curve of the fuse clips. Tedious little job. Easier to do with the harness on the bench. Probably not an option for you...

Just one more note, if you do have to dremel the fuse clips, they are probably so rusted that the finish is gone. You just want to clean them up, not grind a hole. Get a couple little packets of bulb grease from the parts store, and put a thin coat on the fuse clips with a q tip swab. You should not ever have a problem with fuse contacts again.

I'm willing to bet it's a fuse as well. I had a similar problem on my 67, when through all the trouble of putting in a new switch and lo and behold, still had the problem. Crawled under the dash and pushed the loose fuse all the way in, magic!!

so the previous fuse was blown?

You need to get a test light. Even a cheap one for now. You need to pull the headlight switch on, and probe the small fuse you replaced on both sides of the fuse so we know if you are getting power that far.

for the instrument panel the power goes first from the switch to the fuse and then to the panel itself

so the switch gets power from the fuse box, the switch then relays the power to one of the other plugs connecting to the switch, then it goes back to the fuse box, into that small fuse, and then to the instrument panel lights. There's a thread that has the whole diagram.
I think it would be, i mean... if your headlights work and the instrument panel doesn't... its the switch not routing power to everything... maybe a connector is loose or broken, hard to tell.

Link 2 other thread
http://forums.stangnet.com/showthread.php?t=729225

Hmm that is a wierd problem, Do you have a stock alternator? I've heard some alternators don't kick in till they reach a certain rpm. But maybe its something different.