IVR pulse at 4 volts gauges read low

In the beginning, Every vehicle operated on a 6 volt electrical system. All of the components were designed to that 6 volts. When 12 volt systems brought brighter lighting, etc.. a few design changes in components were required.
In the case of thermal gauges, GM was the only mfgr of that time to redesign those instruments so they operated on the 12 volts. Every other mfgr opted for a mechanical voltage limiter. This added component would take in the 12 volts and put out a intermittent or pulse voltage. A bouncing set of contacts may sound crude by todays standards but.. this thing did work very well for a very long time. If it received close to a steady 12 volts it would release approx' 6 volts. Therefore nothing else about the thermal gauges would need redesign. They would work just as they did in the 6 volts systems ( just range indicators afterall ).
What did matter and what didn't matter;
Where the mechanical limiter is located didn't.
The voltage supplied to it and a zero resistance path to chassis ground from it does matter.
Is this owners mechanical limiter simply worn out ? Maybe. it is nearly 50 years old.
Is there a way to test it and/or adjust it so it works right again ? Maybe.
Is replacing it with a solid state regulator that releases a steady voltage the better route ? Of course. For several reasons including extending the life of those thermal instruments that are also nearly 50 years old.