Tim, the device is a fuel tank sender connected to a instrument cluster gauge. The project is to replace the fuel sender (probe) with another one with different Ohm characteristics, but I thought it would be nice to have an adjustable converter that works will any fuel sender within a certain range, and connects to any fuel gauge. They are commercially available, but I can't imagine it being that hard to build.
Jeroen79, so cluster gauge is pushing through voltage/current and moves the needle based on the current reading?
So let's see, we have 2 wires coming from the probe - our 'variable 'resistor'. I'm going to snip those wires and see what voltage is the gauge pushing, and what current is flowing at 0 ohms. I can use a variable resistor to replicate probe's resistance. I would expect the resistance to be proportional with the measured quantity.
I'll be back shortly.