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You are welcome, Keith.
Glad I could offer something of value.
I admire XJNick's troubleshooting technique, but I believe he might
have inadvertently reversed his empty vs. full tank resistance readings.
Thinking through the situation -- With a fuel tank full of gasoline, the gas gauge needle should be at maximum deflection toward the "Full" mark. Gas gauge needle deflection is proportional to the amount of current through the gas gauge deflection coil. No current, such as when the Jeep ignition key is in the "off" position, means no needle deflection. Hence the gas gauge needle points to "E."
This is a simple series circuit: +12 volt battery voltage is reduced to a nominal +5 to 7 volts by the vibrating contact power supply- voltage limiter contained within the gas gauge. Current flows from chassis ground, to and through the variable resistance of the fuel tank sending unit, to and through the gas gauge deflection coil, to the positive 5 to 7 volt output of the vibrating contact power supply-voltage limiter.
Maximum current through the meter movement deflection coil will occur when the variable resistance of the sending unit is minimum.
Ergo: Full tank = minimum fuel tank sending unit resistance (Whatever the designed minimum value). Empty tank = maximum fuel tank sending unit resistance (Whatever the designed maximum value).
Reduced to the essence, your gas gauge is an ammeter with a meter face calibrated in capacity.
Regards,
Inspector-G
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