Low fuel indicator light using MPGunio

[anOkayAsian]

I have the task of building a low fuel indicator light for a racecar that turns on when 25% of the fuel has been used. I was thinking about using flow meters and calculating how much fuel has flowed through the lines, but don't want to add in the extra hardware. I was thinking about using an MPGuino style system where it calculated using the fuel injectors, but I don't know where to start with the programming. The source code I could find is 99% LCD stuff and I don't need any of that, I just want a light to turn on when the injectors have used __ amount of fuel. Can anyone help me out with making this script?

[ECO-AKJ]

Maybe try a sensor like a washer fluid level or brake fluid level or oil level sensor that kicks on a light, and then figure out how much a full tank is and then fill quarter of way and mark spot for level sensor....Just an idea, not tried it myself but have sold a few in my line of work