Question about instrument voltage regulator

yes, when the car is idling, the voltage is dropping down low, this and the fact that the original gauge regulators were electromechanical, that combined with the previous stated ground prob can cause havoc with the setup. If you can find the magazine article called "gauge rage" from the pages of mopar action magazine, this gives the whole lowdown on the fix for the problem. Another good site for some mopar electrical malady fixes is www.madelectrical.com .