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Fuel gauge in a 70's .g.m cars.?

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  • Fuel gauge in a 70's .g.m cars.?

    Hello. The vehicle we plan on taking on the long haul is a 70's g.m. forget the model.
    The fuel gauge in the dash is pegged at full at all times.
    From what I've been able to figure out from never see the car, but looking at ebay add's for the gauges for those cars is there is a single wire that goes to the tank.
    How do you check that it is the wire/ the gauge/ the sender/etc
    I want to have all the info, to test/check the system when we get to the vehicle before we take off for the tour, and hopefully get it working. instead of flying blind.
    Thanks. Car is a few thousand miles away from us. So can't test it or even lay eyes/ hands on it.

  • #2

    Re: Fuel gauge in a 70's .g.m cars.?

    If you can get to the sending unit directly on the tank you can measure the ohms at the sender - I believe most GMs of that era are 90 ohms full 0 ohms empty. IF the tank isn't full and the sending unit reads 90 ohms then my guess would be a bad sending unit. If the sending unit tests good, then hook the wire back up to the sending unit and read the ohms at the gauge (disconnect the sending unit wire from the gauge) - if the ohms are significantly different than it was at the sending unit, then I would suspect the wire.
    Eric likes this.

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    • #3

      Re: Fuel gauge in a 70's .g.m cars.?

      Plenty of 40.00 gauges out there if the sending unit is OK, but you still need to know the range of the sending unit to make it work right. So if you have movement, whatever it goes to when you know its full is the one you have to get. There are quite a few out there. Some GM only goes to 76 or 80.

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      • #4

        Re: Fuel gauge in a 70's .g.m cars.?

        Check the ground wire at the tank, if it's off or broken fuel gauge will peg full.
        Pt 2010, Long Haul 2011,12,13,14,15,16,17, 18, 19
        If you wait, all that happens is that you get older

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        • #5

          Re: Fuel gauge in a 70's .g.m cars.?

          common failure, the sender is bad - granted on a car nearly 50 years old, there's also the Bubba factor, but if it hasn't been messed with - it's likely a bad sender.... which means dropping the tank to replace....
          Doing it all wrong since 1966

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