T3 fuel gauge

[Komorebi]

Hi guys.
Firstly, electrical is really not my thing so bare with me.
My fuel gauge is playing games with me. When the fuel tank is completely full it shows just over half a tank on the gauge. And then run down from there. The goes way past the empty mark while still having fuel in it.
Does anyone know if this is the sender unit or the resistor? I had the sender out a few times and it's clean and looks in ok nick.
Any advice would be greatly appreciated 

[Robsey]

It could be the ring connector on the end of the brown earth wire from the sender getting corroded or dirty.
This would increase the wire resistance giving a lower than normal gauge reading.

Unscrew the brown wire from the van floor.
Cut off the old ring connector, and
Crimp on a new clean one.
Check that the self tapping screw that fixes the ring connector to the van floor is clean and securely fitted.

[silverbullet]

Or the voltage regulator has failed (the transistor on the foil pcb) whick will then give you false readings.
Does the temp gauge read about right?