Dash is out - 66 Val

You're going to need at least a test light to diagnose it. You need to test for power at the fuel gauge to see if the voltage limiter is working. The attaching nuts for the gauges can come loose or get a bad connection even though they look good. Use a nut driver and work the nuts back and forth to gain a good connection. The ammeter is completely separate from the rest of the gauges so you'll have to test it alone. The factory ammeter is hot all the time on both posts so be carefull to disconnect the battery when you pull the cluster loose from the dash. If the gauges have power it's probably the sending units that are bad (the most common problem) You can test them by disconnecting the sending unit wire and jumping the wire to a good ground. Turn the ignition to the on position and see if the gauge(s) now work. If so, turn the ignition back off right away so the gauges don't peg at the max position as they can burn out if you let them stay there too long. If the gauges move, the senders are bad. If they still don't work, you have another wiring problem from the dash to the senders to chase down.