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Testing gas gage & sending unit out of car

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  • Testing gas gage & sending unit out of car

    I have my M 5 apart & ready to paint.
    Both the gas tank and dash are also out of the truck.
    I am putting a 12 volt gage and sending unit in it.

    How can I test them?
    Can I supply a full 12 volt to the gage?
    If not please advise.

  • #2
    You might get a better response if you post this on the technical forum

    Leonard Shepherd


    • #3
      I don't think you want 12 volts going into the fuel tank. On my 67 Charger and 59 Impala the fuel tank uses 5 volts going to the sending unit in the fuel tank. Both of the 12 volt cars has a limiter at the fuel gauge that limits the voltage to 5 volts, and my guess is for a safety factor. I have a 50 model Stumpjumper, and that gets the 6 volts to the sending unit, so I can only give you my experience with my other cars.


      • #4
        If this is an older style gauge that uses a full 12
        The hard way...
        Gas tank senders are the ground for the gauge. The variable resistance on the float mechanism varies the voltage going thru the gauge and registers the height of the fuel.
        If the gauge is the older type, run the +12 to the proper stud on the gauge, then a wire from the other gauge stud to the isolated stud on the sender unit. Ground the gauge cannister and tank flange with another wire. You can then move the float and see if the gauge registers.

        The easy way;
        Use a VOM to see if the resistance changes on the sender while you Move the float. That's one side
        Apply +12 to the (+)gauge stud and connect the other stud to the battery ground. If it swings full scale, it's ok.

        Bob Johnstone
        64 GT Hawk (K7)
        1970 Avanti (R3)


        • #5
          Thank you all.
          I am done with it.
          Test it OK.