Light only comes on when you have less than 10L left, mine came on for the first time last week. What lead you to believe the fuel warning light was faulty? Did you run the car to empty with no warning or is it just the gauge, if its the gauge don't be alarmed, pretty much everyone on here with 33s has the same problem and from what i can remember its from a dodgy fuel sender which has more than likely fallen off its perch inside the fuel tank, this is why you get weird readings (mine never reads more then 3/4 full even when i fill it up and will sit there for about 200km then work its way to empty).
If you did run it empty... well then your in for all sorts of fun with that Otherwise just fill it up and reset the trip meter, drive it for about 300km and fill it up again, note how much you have to fill it up to get to a full tank again (full r33 tank is around 65L) so say you did 300km and used 40L well next time drive till 350km and see how much to fill up a full tank, repeat until you are left with 10L at refill (leeway for occasional hoon behavior ) and just remember to reset the trip meter every refill and drive till that set kms (I fill up and drive 350km before heading to the local BP)
Or if you want to be gung ho and not a lazy sod, you can pay someone to fix it and not worry about any of the stuffing around remembering numbers