This is from memory , I'm no auto electrician. I think the IGN warning bulb Voltage rating needs to be lower then the nominal Voltage rating of the whole system . For a 12V system the IGN warning bulb is something like a 8V bulb , because the IGN warning bulb only "sniffs" the charging system , it doesn't get the full 12 Volts.
This might help
https://www.howacarworks.com/ignitio...-warning-light