... how do i make a Wheatstone bridge circuit?...
Before I launch into it, let's get some things on the table.
1. Which, specifically, sender do you intend to use?
2. What will be its resistance tank empty?
3. What will be its resistance tank full? You cant answer these 'till you actually mount a sender in your tank!
4. How many steps will it make full-to-empty? A float-arm sender has continuous varying resistance.
5. The power source is an 12V alternator/battery system? ~12V parked? 14.2V engine running?
6. I presume you want to make the fuel gauge immune to voltage changes engine stopped vs engine running? You want to average out sloshing in a moving boat?
7. You are hell-bent on having a digital readout instead of an analog meter?
8. You are willing to mentally move the decimal point if the digital meter reads 10.0 for 100% full?
9. You are willing to build a circuit which uses some 1% resistors, a couple of electrolytic capacitors, a voltage regulator, a dual opamp, and one of those Ebay voltmeters?
10. You are willing to settle for two point calibration (Full and Empty)?
11. What have I forgotten?