pegged out fuel gauge/Dual fuel tanks
Fuel gauge is maxed out no matter which tank is selected. Front/Rear. If it were the sending unit then one of them would be accurate but its not.Just bought truck and it was almost on empty so I filled the rear tank and afterward the gauge pegged out way past full.switch to front tank and its pegged out.HELP Please.
The wire going to the sending unit is grounded. -- The fuel gauge is a volt meter with a different face. Twelve volts come in one end and the sending unit changes the ground potential. The changing potential allows the needle to move. When the ire is grounded, the gauge sees zero volts and the needle swings full range. BTW - all electric gauges are the same. Different faces and ranges but all voltmeters.
Ford had a lot of trouble with the switching valve in the frame, it would switch tanks but the sender part of the valve assembly would go open so you would not get a gauge reading, I don't believe the valve is available from Ford any more but you should be able to get one aftermarket. Ford went from a IVR voltage system to a magnetic system on the fuel sender system so if you lost connection with the sender the gauge would go full scale just like a GM.
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