1968 Barracuda with internal gauge régulator

You can easily figure it out. Look at the traces on the PC board. Follow the gauge studs / traces

1.....One gauge stud goes to a harness connector pin

2.....A second stud goes to a second connector pin

3....The third gauge stud has an insulator cap

Get your service manual/ ohmeter, whatever. Figure out which of the two that go to the connector pins go where

One of the two harness connector pins goes to switched 12V

The other of the two harness connector pins goes to the sender

The gauge stud with the cap is the "jumper" that feeds the VR OUTPUT out of the gauge and to the other two gauges.

So your new regulator needs ground...............

it needs switched 12V

and the output needs to go to the stud on the cluster with the cap