Cornmuse,
The sender unit is in the tank. You can see the top of it if you pull out the carpet. Anyway, the"low" light on later cars comes on at about 2 gallons remaining. And yes, when it gets towards the bottom they seem to go bonkers. My current car is OK but I was about to pull the sensor on my last and carefully clean it with solvent. It is a resistive circuit and I understand they eventually get crudded up.
I live North of you in the Coachella Valley. Fuel prices are usually better here. However, feel MY pain! I drive a 12 cylinder 390HP, '97 Coupe with a 27 gallon tank and get 19 per gallon on trips and almost nothing around town with the AC on. While you are saving money with your CD I am having the time of my life with this powerful "brute". How long does it take your CD to go from 80 to 135?
Anziani
'97 CL600 51K