This is pretty simple, a lm3915 is a 10 part voltage comparotor, this means it will will take in an analog voltage and turn on 1-10 of its pins based on how larger the voltage is compared to reference. This means that if you use the "sender" and a 100 ohm resistor in series (I dont think 90 exists, try to get closest to 90 you can) and your car battery voltage divided by 2 ( use a resistor voltage divider here to) as a source, it will divide it up 10 times based on the voltage accross the resistor. Larger the resistance of the "sender" bigger the voltage drop accross the 100ohm resistor and the lm3915 will turn on one pin at a time. To make it "count down" use pnp transistors such as (2n2222) at every out put pin and you'll get your desired effect