So I have no power to the glow plugs. New battery.Changed 104 relay still no joy. Preheat light is on. Plugs are good. Am I right in thinking that the coolant temp sensor decides if power is needed to the plugs? Anything else can try? I am slowly going mad...... when I changed the relay the buzzer sounded when the lights are left on and the ignition key is removed. It hadn't been working for a few years. It started to work then stopped. Not sure if thats related or not???