I'm unsure how to bring in the input from the fuel guage so when the voltage at the fuel guage drops to the 3V the output of IC 1A goes high.
On the attached diagram would I need to connect the fuel gauge voltage at the + input of IC 1A (not requiring R1 and R2 as shown) and then adjust RV to 3V? So in theory when the + input of IC 1A drops to 3V, it matches the input of 3V controlled by RV at the - input of IC 1A which makes the output go high?
As far as the 12V light, can I just connect it directly to the output or would I need to consider a transistor & relay configuration?
Since LM393 has 4 comparators and I will be using 1 of them, do any of the other comparators need to be tied to voltage as well to prevent "floating" ?
they have much to do with the voltage falling and causing the light to function.
from what i understand you may need a constant +12v and the adjusted voltage from gas sending unit on the inputs of the comparator to give you the needed output
i also looked here to get a better idea of what this IC does.
worse comes to worse you can always get a arduino nano to do what you want!