You can bench or semi bench test your LFW Module. You need a potentiometer capable of zero to 100 Ohm's, and if out of the vehicle a test light to act as the FUEL warning light. (battery operated test light is easier)
When triggered by low Ohm's the module drops ground onto the yellow lead so the bulb which always has power, then has a path to light up.
To test the LFW Module in place by dialing down to less than 10 Ohms (eighth of a tank.) if there is no ground on the yellow wire at that point lower toward zero and see if you get the ground on the yellow activating the light. Make sure you have power on the bulb lead and the bulb is in good order as well.
Brian