try to start car but dies

Hi, my name is Devin. I am an auto repair expert with the Car Genius team here at RepairPal. I’m sorry to hear you're having trouble with your vehicle. Since your Mustang won't start and you hear a single click sound, I would begin by inspecting the starter and starter relay. A failing starter relay could cause a single-click noise and prevent the car from cranking. You may also want to check the wiring connecting to the starter for any damage or corrosion. If you need more advice, have any other questions about your vehicle, or would like to get connected to a RepairPal Certified shop near you, we have you covered. Give us a call at 877-913-1554, and we will happily help you out!