'86 duel tank GMC Gas Gauge issue

Discussion in '1973-1987' started by Ken Hepting, Oct 10, 2018.

  1. Ken Hepting

    Ken Hepting Member

    Oct 10, 2018
    When either tank is full fuel gauge reads 2/3 to 3/4 empty. Hence, I never know when reading "empty" really means, "EMPTY".

    I have replaced (1) tank sending unit, dash switch and fuel distributor-switching unit with no success.

    I suspect the gas gauge needs replacing since it indicates both tanks being faulty readings????

    Thanks for any input.
    Last edited: Oct 10, 2018
  2. nerfherder78

    nerfherder78 Member

    Aug 15, 2003
    Fairfield, CA
    Most likely the resistor on the back of the gauge:
    The GM Fuel Gauge Mystery 1965 & Newer |
    Pull it off and see if the gauge moves.

    There are 5 different color resistors, you'll want to replace it with the same color:
    Lt blue-123 ohms
    green -89
    blue black-81

    I had one fail on the back of my voltmeter last year, threw me off when I looked down and saw 0 volts. Managed to find a replacement after scouring the local wrecking yard.

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