Mick wrote:
The tank sender is grounded against the fuel tank by the metal on metal contact of the retaining clip. The fuel tank is grounded by its contact with the body. Both these ground contacts are purely unintentional, as the sender retainer was painted and not physically screwed down, the fuel tank strap once had a cork gasket between it and the tank, and the tank itself once sat on a piece of hessian.
What all this means is that the tank being connected to ground by its own physical contact with the chassis was not a guaranteed proposition, the black wire on the sender is instead a known good earth to make up for this.
So...yes it doesn't specifically need the black wire, but it's good electrical practice and prevented potential warranty issues to provide one.
Use a multimeter as it was spelled out in an earlier post to measure the resistance the sender provides for the float in the full position and the empty. This will decide the problem.
oh ok I see. I don't have a multimeter so I was just trying to see if I could fiddle around some more to solve the problem. Looks like I will have to go see a mate who has one in the next week or so, and check it out. Thanks heaps for the advice Mick.
Cheers Lockie.
It's the boobs and testosterone that make this place fun-ner 
!! 
That's the first thing on my shopping list for tomorrow now 
Thanks heaps guys