The gauge posts have to be correctly wired for the gauge to read correctly. i.e. Input and a output
The sending unit should show with full tank of gas 30 ohms.
You can test just the gauge without the sending unit connected.
You can use the 6 volt charger to do the test.
Connect +6V to the gauge power terminal. Connect the battery negative or ground lead to the gauge mounting plate. At this point, the gauge needle should go to "full" or beyond. Now connect the gauge sender terminal to ground (or the mounting plate). The needle should go to "empty" or beyond.
If you get the above results on both the sending unit (30 ohms) and fuel gauge shows full with 6 volt applied and it still doesn't work.
Check for bad wire connections and a bad ground connections at sending unit.
If still no go check wire to sending unit..
1949-53 Shop Manual Fuel Gauge Testing Sorry I don't have a KMO-204 gas gauge tester. But I would like to have one.
Tech Tips:
Gas Gauge Problems I still would use a Runtz-style resistor Gas Gauge Voltage Reducer.
That stuff was designed to be used with 6 volts
