How do you know if the glow plug relay is bad?

You can determine if the glow plug relay is bad by checking for a few symptoms: if the engine has difficulty starting, especially in cold weather, or if the glow plug indicator light on the dashboard does not illuminate. Additionally, using a multimeter to test for continuity can help; if there’s no continuity when the relay is activated, it’s likely faulty. Finally, you can also listen for a clicking sound from the relay when the ignition is turned on, indicating it’s functioning properly.