Possible sender fault

TOY440 said

.....I disconnect the feed wire from the sender......and it still reads full, I earth out the wire, it reads empty but very very slowly creeps towards full.

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Sorry this does not make sense. Dana67 ^^ above is correct. When the sender is "full" the resistance is low, causing more current to flow in the gauge. Here are the factory tester values



I would re-test.......perhaps you did not get the sender wire well connected to ground.