Well, Lucas is said to be called the "king of darkness". When one is making lights, this is strange. I suspect the wiring coming out of your sender unit. They rust coz of their location. Take your fuel gauge out and wire it this way: Negative to negative of battery. The other pin just put 12 v to it. It should indicate full. That way you'll make sure the gauge is or not your problem
Younger, we pointed the lad I now became.