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Does polarity of fuel gauge wires matter?

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    Does polarity of fuel gauge wires matter?

    My fuel gauge didn't work, so I swaped the wires. Then the gauge showed the tank was full, and I was happy. But now it seems the gauge always shows full, which isn't exactly what I intended.
    GS1000G 1981

    #2
    It's just a variable resistor so it shouldn't matter. Can you see if the float is moving?
    2002 bmw r1150gs 1978 gs1000E skunk les pew 1979 gs1000L dragbike
    82 gs1100L probably the next project
    1980 gs1000G the ugly 1978 gs750E need any parts?
    https://m.youtube.com/watch?v=m_m2oYJkx1A
    1978 gs1000E skunk #2 RLAP

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      #3
      As Eli69 says, it's just a variable resistor. The fact that it shows a full tank wired one way and nothing when wired the other way suggests that there is a short in the resistor. You can remove the sending unit from the EMPTY tank to inspect the windings. You can also connect an ohmmeter to the leads to verify smooth action when you move the float.

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        #4
        Originally posted by Noreg View Post
        My fuel gauge didn't work, so I swaped the wires. Then the gauge showed the tank was full, and I was happy. But now it seems the gauge always shows full, which isn't exactly what I intended.
        If you have the OEM workshop manual from the BassCliff site, there is a detailed section on testing and troubleshooting the fuel gauge and meter in the Electrical System section. Pages 262/454 to 266/454 in the PDF or actual page numbers in manual are 12-23 to 12-27. Note that the manual calls the section inside the revcounter the "meter" and the part inside the fuel tank the "gauge".

        The tests describe how you determine if it is the meter or the gauge (float portion inside the fuel tank) that is defective. The fact that the needle of your fuel indicator now always shows full after you swapped the wires, shows that that part is working and your problem is at the float unit inside the fuel tank. Very often the problem is caused by a loose wire or poor contact at the variable resistor part of the float inside the fuel tank.

        On the BassCliff site there is a "Fuel Gauge send unit repair" document by member Jethro. I have it in PDF version - cannot upload it here - send me a message if you cannot locate the document.

        EDIT: The page numbers I quoted above are from the 850 manual.
        Last edited by 2BRacing; 08-15-2021, 07:18 AM. Reason: Clarify page numbers are from 850 manual.
        1981 GS850G "Blue Magic" (Bike Of The Month April 2009)

        1981 GS1000G "Leo" (Bike Of The Month August 2023)

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          #5
          No electrician but... If wires hooked correctly & gauge shows one thing, then wires hook other way & gauge shows something different, that should answer if polarity of fuel gauge wires matter. If it didn't matter, gauge would read the same wired either way...I think.
          1983 GS1100E, 1983 CB1100F, 1991 GSX1100G, 1996 Kaw. ZL600 Eliminator, 1999 Bandit 1200S, 2005 Bandit 1200S, 2000 Kaw. ZRX 1100

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            #6
            Originally posted by rphillips View Post
            No electrician but... If wires hooked correctly & gauge shows one thing, then wires hook other way & gauge shows something different, that should answer if polarity of fuel gauge wires matter. If it didn't matter, gauge would read the same wired either way...I think.
            Unless there is a problem with the wiring in the sending unit. If the winding of fine wires has broken and one of the loose ends is grounded, it will show as a full tank when the wires are connected in one direction. When the wires are connected in the other direction, the gauge only sees the open wire, therefore NO reading on the gauge.

            Probably not a common occurance, but it is possible.

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