I would suggest measuring a 12" section of the wire, dividing that by 12 and look up nichrome resistance wire resistance per inch. There are two different primary compositions of nichrome, find the correct gauge and class. Then you need to rewind the sender with the appropriate length and number of turns of wire.
To be honest, I am working on something very similar on my Mercedes, and not familiar with your car, but the theory is pretty much the same.