MG Car Repair: MGB Fuel gauge wont operate, voltage stabilizer, gauge needle

Question
I have a 69 MGB with a fuel gauge that will not move as the tank empties.  

When  the ignition is turned off the needle returns to empty.  When the
ignition is on it shows full, even when the tank is nearly empty.

I purcased a new sender unit.  To test it I disconnected thed current unit and
attached the two leads to the new sender.  Same result.  Movements in the
sender arm have no effect on the gauge.

The temp gauge works, so the voltage regulator seem sto be working.  

Any suggestions?  

Answer
Hi Gene,
If the other gauge works normal the voltage stabilizer is probably ok as you have indicated. A rough but effective test of a gauge we used in the dealerships was to just turn on the ignition switch then remove the wire from the sending unit and the gauge needle should deflect all the way. (I don't remember which direction but that doesn't matter) then ground the sensor wire and the needle will deflect all the way in the opposite direction. If the gauge does not do that it is faulty or disconnected. So check the connections including the ground wire at the gauge (black)

Let me know,
Howard