This configuration with the LM111 was found in your factory manual. The circuit can be implemented with modern operational equivalents. The power supply must be symmetrical.
If the input voltage falls below 12 V the LED glows up. Other voltages can be monitored by...
ON Semconductor FFSP0665B 650V 6A SiC Schottky Diodes Available through Mouser Electronics, these...
This adjustable circuit from 0 to 200 nA was found in a 90's EDN. The components can still be...