Test the sending unit with a multimeter set on ohms. Connect the black lead to ground and the red to the terminal like in the pictures I attached. This is an old one I have for the Chevelle. I'm pretty sure yours is 0-90 ohms like mine is but it might be 0-30. When the tank is full (arm up) it should read 90 ohms. When the tank is empty (arm down) it should read 0 ohms. As you can see mine is a little off.
