instrument cluster voltage limiter

In the beginning all vehicles had 6 volt charging systems and gauges.
When the 12 volt system came alone, mfgrs were faced with 2 options. Build 12 volt gauges or limit the power to 6 volts for the same gauges. 90 % opted for the 6 volt gauges and a voltage limiter. GM is one of the few who went to 12 volt gauges.
Those early 12 volt gauges produced almost constant needle movement.