1970 Ralley Dash Voltage regulator?

Sorry I don't understand. The IVR on "most" (non Rally) clusters is a separate part. "Back in the day" (Ford and AMC used 'em too) was before good solid state circuits existed. The gauges have a natural mechanical delay and are slow to move. The IVR works like a signal flasher, pulsating. This supplies an on/ off signal which "approximates" 5-6V You don't see this because the gauges move slowly

The difference (I don't know WHY) in the early cars and the ralley dash is that Ma decided to build the IVR INTO and unitized WITH the fuel gauge. It is normally not servicable, nor replaceable. "If it failed" back then, you would have to buy a complete new fuel gauge.

Nowadays, guys "hack into" the gauge, disable / remove the old IVR and "hitch" an external one outside.

Here's a read:

http://rt-eng.com/rte/index.php/RTE_Limiter_Faq

http://www.forabodiesonly.com/mopar/showthread.php?p=1970284036

http://www.forabodiesonly.com/mopar/showthread.php?t=191062