Gauge Cluster Issues/IVR

I have my dash apart on my 68 barracuda I am testing for continuity between circuits on the PCB. I have hooked an alligator clip up to the positive on the oil pressure gauge and then grounded the pins leading to the negative of each gauge oil, temp, fuel. The temp and fuel gauge sweep but the oil gauge does nothing. I have also tested the gauges out of the cluster But still cannot get the oil gauge to sweep? I guess it is busted?
But the main questions I have (see pictures) is how do the oil temp and fuel gauge get a positive feed? from the looks of the circuit they all are connected via a common circuit.
(In one of the pictures I have an alligator clip hooked up to the positive terminal of the oil gauge) you can see the circuit connects all three gauges positive terminals, but where do they get power from? Is there a positive wire that hooks up to one of the terminals?
Also in the picture I have a red pointer that is pointing to the positive of the temp gauge the last terminal is the fuel gauge. Why does the fuel gauge have three terminals and what is that black wire for that leads to (a condenser?)

Finally I cannot find Instrument Voltage Regulator did all cars have a IVR ?

Thanks Everyone

Barracuda Guage Cluster.jpeg

Gauge Cluster with Clip.jpeg