I just resolved this issue on my 90 Celica All-Trac. Here is how I did it:
From one of my other posts....
viewtopic.php?f=10&t=54225&start=15#p496190
First post: "I removed the fuel level sender unit and noticed that the low fuel level sensor on the bottom of the second arm is missing. Is this part still available for sale? Does anyone know if another sensor from some other Toyota/Lexus will work?"
Second post: "I got a fuel level sending unit on Ebay that was for a 1998-2002 Toyota Corolla. It looks as if I can get the low fuel sensor that comes with it to work with some cutting and splicing."
Third post: "I finally received the fuel level sensor and low fuel light assembly from the Corolla. I cut the low fuel level switch/sensor off using tin snips and also cut the wire and stripped it about 1/4 inch. I then put the switch/sensor where the original one was and bent the part that holds the sensor, the bottom of the metal arm, with some pliers to make a nice pressure fit of the new switch/sensor to the arm. I then soldered the wire to the original wiring and used some heat shrink.
Then, I went out to the car and plugged my nicely refurbished All-Trac fuel level sender in. I turned the key to the ON position and within a few moments the LOW FUEL level light illuminated! Then I moved the fuel level arm all the way up and the gauge on the instrument cluster slowly moved to the F position!!
Finally, I then wanted to verify that the LOW FUEL level light would extinguish itself when submerged in fuel. I cut out a hole in the bottom of a nearly full fuel injection cleaner bottle and then submerged the low fuel switch/sensor in the bottle. After a few moments, the LOW FUEL light turned off!!!
Now I am going to put it all back together and hopefully have a nice running All-Trac."