'84 Fuel Gauge issues

[Bob Q]

Recently the fuel gauge on our '84 K2500 diesel started pointing past full at about 3:00 regardless of which fuel tank is selected. Do you think this sounds like a bad ground or a bad gauge? I unplugged the weatherpack harness at the valve and plugged it back in thinking there might be corrosion on the terminals, but no luck. Since it's happening on either tank, do you think I should trace the wire from the B terminal on the valve weatherpack back to the dash and see if the issue is there, since from what I understand from Hatzie's dual tank theory thread below, that is the common sending unit wire back to the gauge?

Thanks.