Could be a knakcered sender.

I know when i first got my cabby on the road though the gauge didnt work and i ran out of petrol every day for 10 days, so i fixed the sender as it was stuck, but then it would cut out well before the petrol light came on in the instruments, the one way valve was also knackered in the pump, and the pump was whining its tits off too!

Since changing my pump and one way valve its not been an issue since it runs forever and a day with the light on!