69 Dart dash volt regulator

Just the IVR? doubt it. You would have to simulate the load of the gauges.

Here is some of what goes wrong..

Obviously the IVR itself

If only one gauge works or seems inaccurate, the gauge unit

gauge sender

wiring between

ANY connections, including the wire end to the sender

At the dash, poor connections at the cluster connector and broken / loose pins on the circuit board

Also, bad connections between the IVR contact fingers and the printed circuit

And loose / corroded nuts on the dash instruments.

You can see, that after 40 plus years, "it adds up."