Gauge help !!! Please

I thought we controlled both gauges by regulating the negative side through a variable resistor or sending unit. What it looks like is the negative side of all the gauges somehow got tied directly to ground. If our ground is functioning through the resistor or sending unit it won't matter how much voltage we run to the gauge. We can prove this by taking the wire from our sending unit and grounding the wire. The gauge will peg. This should be true with oil pressure, temp and fuel level. So if the voltage limiter isn't the answer you have another tree to bark up.