I made some measurements.
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I disconnected the fuel level sender from the gauge and measured voltage between the gauge wire and ground. Voltage was 6,86 volts.
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I then measured resistance between same wires (turned off the power). It was 66,6 ohms.
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Then I measured resistance between two contacts of the fuel sender unit. It was 58,7 ohms (i guess it means, that the tank is half full)
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Then I connected fuel gauge back to the fuel sender unit and measured voltage from the same wires (ground and gauge/level sensor wire; power on) and it measured 3,39 volts.
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I then decided, it would be nice to check the current flowing through the sensor too. It was 0,0556 amps.
Added some paint-made illustrations, hope it will help.
