Failed fuel sender?

[Ceejay 72]

Having completed my change of fuel tank, I find that the fuel gauge does not work correctly any longer - it goes to full deflection when the ignition is on.
There is voltage at both the live terminals on the sender and the earth terminal works.
On removing the sender unit, I found that the position of the float makes no difference to the gauge full deflection. I would have expected to be able to measure a change in resistance across the level terminal and earth with varying positions of the float, but there is no change - it's just virtually maximum resistance. The warning light terminal on the sender appears to do nothing either.
Am I correct in assuming that the sender is U/S? There was no disturbance to the wiring during the tank change.

Thanks,
Chris

[DZP]

Hi Chris,
I would have expected the fuel gauge to read empty if the sender was open circuit (maximum resistance).
Are you sure you have the gauge and warning lamp wires connected correctly?
The warning lamp is a straight 12v from the Ignition, but the fuel gauge takes 10v from the voltage stabiliser, both rely on the sender to provide an earth connection.
A voltage stabiliser issue would also cause problems with the temperature gauge.
Warning lamp connection pin is ground when the tank is empty
Fuel gauge connection pin is ground when the tank is full.
Regards,
Den

[trunt]

Sure you have the correct terminals on the sender dentified?

Agree with Den, you say "it's just virtually maximum resistance" for the gauge to read full it would need to be Minimum resistance... so the sender wire is grounded.. I would check again..

Disconnect the sender wire - the gauge should go to empty..
short it manually to ground it should go to full..
short the indicator wire manually to ground, it should light the warning lamp.
If all thats OK the wiring to the sender is OK.

Then make sure you are connecting them correctly..

[Ceejay 72]

Thanks Guys,
I checked that the connections were the right way round - they were. Swapping the leads over, the gauge went to zero.
The sender wire disconnected, gauge went to zero, shorted to ground, it went to full.
Shorting indicator wire to ground did nothing, so I guess the bulb has failed.
Thanks for your help!
Chris