Here is a schematic.
Input connector and Power Supply
CONN1 is a input connector. From CONN1 connector get power a circuit and as well measure input voltage. Input D1 - D4 diode's are connected in Gratze bridge, this is important to we have always correct polarity power supply to the circuit. Power supply is standard 78L05 IC and couple capacitor.
R1 and R2 divide input voltage to A/D working voltage range. In this resistor setup you can use till 20V. If you need higher or lower input voltage range, you need to recalculate R1 and R2 value.
PIC12F675 - A/D Converter, Comparator, LED Driver
In PIC running the Anderson Powerpole Polarity and Voltage Tester software. The software is written in JAL programing language. First read A/D converter, after compare A/D value with user defined comparator toggle levels and finally pull down to GND LED's Cathode.
"Display" Bi-color Led
Whit one bi-color led you can read status of the comparator.
Default Comparator Trigger Levels and led colors:
Low Voltage (Amber/Orange Led) - <11.5V
In Range (Green Led) - >11.5V - <15V
High Voltage (Red Led) - >15V
Wrong Polarity - Flashing Red Led