The wire on the top of the fuel sending unit that runs to the gauge cluster, should go through that round bulkhead that you disconnected.
If none of your gauges work, I would recommend replacing all of your tube fuses. I ran my '73 Scamp with old fuses, even after an engine rebuild and just by changing out the fuses that still worked, I ended up gaining 3 volts at the dash input power supply wire/ ammeter and lost the headlight dimming problem.
Also, while you have the cluster out, check and see if the ammeter/ charge gauge studs are loose. They are peened/ crimped into the gauge itself and come loose from heat when the wiring has a lot of corrosion in the bulkhead connectors. All of your car's power runs through those two posts, which attach to the bigger wires that have the eyelets on them.
If those studs are loose, you can see as much as 4 volts drop between each side. If they are loose, pull the gauge out of the cluster and solder the studs into the metal that they are crimped to. Use a lot of flux and sand the hell out of the areas.
Even if you end up replacing the gauge for one that has a good crimp/ peen connection or if yours doesn't move, I'd still do this mod, because it is a problem on just about every Chrysler product from this era and can lead to things like wiring harnesses burning cars to the ground.
Also, there is a large red, yellow and blue wire running to the steering column, into a flat bulkhead connector. A lot of the time, there are overheating issues that melt these up. Its usually a good idea to bypass the bulkhead with some soldered bullet type connectors on the three large wires. Those go to your ignition.
There is also a voltage limiter that plugs into the back of the ciruit board. That drops the voltage down for all of the gauges and if it's bad, it can cut all of the power to the gauges.
You can get a replacement voltage limiter at most auto parts stores.
