how to make fuel gauge show proper amount of fuel
Well, of course, you can get a replacement gauge, there's places online who specialize in old car parts, do a Google search. Or, just calculate your fuel consumption by the number of miles driven. I imagine your odometer still works fine. So, if you get 15 miles per gallon and drive 150 miles you've used 10 gallons. See, you don't have to run out of gas, wasn't that easy! On such an old car as this, I might just skip fixing it and save the money towards a new vehicle.
If the gauge swings past the fuel mark it is telling you there is a open circuit in the fuel gauge circuit, it could be a broken wire but usually the sender is the problem, check aftermarket, they may make a replacement by now, or have a universal that can be made to work using different resisters in the wiring to correct the ohms to your gauge. You could try a dealer, but that old it is doubtful that they can get it. You could take a chance on a used sender from a wrecking yard if all else fails.
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