The gauge calibration is controled by what we used to refer to a ballast resistor within the gauge circuit. Now I think it is located near the flasher unit on the peddel box. Small rectanglular alloy box with a couple of wires on it. I know that on my old Fords if these failed they would make the gauges read incorectly though I have never heard of your situation. I would try changing that unit first. I hope someone else can give you the correct name for it. I hope you don't have a problem with the circuit board as they can be expensive to replace or repair

I had a similar thing with my aftermarket gauges. Turned out I needed another ground from the gauge to near the sender. Not sure if this helps.

no it's not erectile disfunction...

The fuel gauge and tempreture gauge on my Datsun 1200 (coupe dash) has recently started to read full alll the time even when disconnected! has anyone encounted this problem with there's?
and what's the solution...
It was reading fine untill this started happening.
Thanks for your help.