The light fades on and off is because of the petrol in your tank is getting splashed around, so sometimes it hits the sensor and sometimes is not.
Then when your tank is almost empty, it doesn't matter how much it splashes, because there's not enough to hit the sensor and that's why the light stays on.
But I'm definitely sure the petrol tank is 65L on R33's and R34's. Because I've tested it myself countless times (not with a jerry can tho lol).
If you car is really thristy on petrol and takes 15L/100km, then you can still get 430km out of a FULL tank.
So for those people who say they can only get 250km out of a tank, then this might make you feel better
Because to be getting only 250km out of a tank, then your car would be drinking 26L/100km lol.