I am working on a 1979 Little Red Express and the gas, temperature and oil pressure gauges do not work. Previous owner bypassed the amp gauge (I assume it took a crap). I pulled the dash. The circuit board is in excellent shape. Dash has a good ground (D pin). Dash lights work. 12 volts to the voltage limiter (C pin) but at the 5 volt side, the voltage is all over the place (0-5 volts and everywhere in between) constantly fluctuating. Replaced the voltage limiter with one out of a working dash and still the same. I am at a loss on this one.

 

The amp gauge is always a problem, Check out this for details. Mine was starting to heat up but cleaned and ran better wires with soldered connectors on the wire, Works like new now. Are you checking voltage with the gauges hooked up? Some reading on the regulator