Instrument cluster regulator

If you get your wiring diagram and trace out the pins on the dash you will see which wire does what.

You can also trace out the PCB from pin to each guage and indicator light.

Ultimately you will be supplying 12v to the 12v pin. Then testing the guages as you did while they were out. (Minus the power you supplied to the guages when they were out as the 12v feed and the regulator is doing that now)