I asked this same question to eight different automotive electrical shops.
Everyone of them said to use the Runz reducer. They told me that it is not a dropping resistor but a voltage regulator instead.
They also told me that the supplied voltage didn't just affect the gauge but also supplied voltage to the sending unit.
This made sense to me so I bought one and installed it.
I checked the gauge and it read accurate at empty, 1/4 tank, 1/2 tank, 3/4 tank, and full.
With the engine running it supplied 7 volts to the gauge. I couldn't be happier with the results.
