67 Barracuda dash wireing

If you have the dash panel out test everything on the bench. You can supply 12 volts and ground to the gas guage then check your temp, gas & oil pressure by temporarily grounding their negative lead (better if you use a small resistor value in series). You can also check all the bulbs. While you're at it pull the fuse block down, pull all fuses, give it a blast of WD-40 and make sure everything is making contact. It would also help to check all your connections at the firewall, especially the fat black & red wires which supply main power through the ammeter.