Bad Fuel Consumption

when does the fuel light come on?
on the 2005 jimny with the new interiors, the spot where the bulb is wasn't visible until it lit up. took me a few tanks of "risking it" till i finally found out it did have a warning light.
on my current 2000 jimny with the old dash, i still can´t see the spot for the bulb, and i've let it go down till it very nearly touched the red indicator. still no light. the most i topped it up with was 36,4L and still no light. does it have one or is mine dead?

mine is 2001 no indication light
so it don't have one or its not working
i have run my dry

Thanks for all the replies guys, pretty much done and checked everything everyone has mentioned.
I'm good with the mechanical side of things but when it comes to electricals it's quite involved, thinking it's the coolant temp sensor as I have looked at it and she's not looking pretty, so I'll just be dropping it off at the mechanic I think

Cheers

There is no light on the earlier models, on the later models the light comes on when the tank is less than 10% full.