Shut down engine when temp to high, oil pressure to low or RPM's too high
It's called "wired OR" and you get it basically for free:







simulate this circuit &ndash; Schematic created using CircuitLab

You can have any number of contact-closure sensors on the "Sensor Bus". If any of them closes, you'll trigger your latching relay to shut down the engine. Of course, before you can restart it, you'll have to clear whatever fault triggered the shutdown in the first place.