how far shall my swift 2004 run after the fuel light comes on

Argee 100% with tennisshoes.

Yes, of course it is best to fill the tank at 1/4 or higher. However, in the odd case of closed petrol stations or roads to them in remote areas, it can be helpful to know this. I can tell you first-hand that the one time I found myself in such a situation, I was able to go an additional 29 miles once the petrol light came on in my 2009 Suzuki Swift. Of course I do not recommend letting it go that far, and other than this instance, I always fill my tank when it goes below half. Of course each vehicle is different, and mine has also been very well maintained. But I hope this is helpful. And I hope you never find yourself in such a circumstance.