The possibility of overheating the fuel heater (glow plug in fuel) certainly does seem worthy of consideration. Fire under the hood is not an option. I have seen posts somewhere that mentioned different schemes to prevent overheating. I will need a relay to switch the fuel heater and that relay should be energized by a circuit that is powered only when the engine is starting or running. Any suggestions for which circuit to use? The glow plug circuit could be used during starting but would not work while running.

Maybe I need two parallel power circuits with two relays. One would be energized with the glow plugs and one while the engine is running. Need to keep it simple, also need to keep it safe.