Why is the lock indicator on dashboard flashing when car turned off?

Hi, this is Bo, an auto expert on RepairPal's Car Genius team! That flashing lock indicator on your 2007 Mercury Mariner’s dashboard when the car is off is actually a normal part of the vehicle's security system. It’s your car’s way of saying, "I’m locked and secure!" Since you mentioned the battery was dead before, it might’ve just been reset, and the light is back to its usual routine. As long as the car locks and starts fine, you’re good to go. If it starts acting weird, like not unlocking or starting, then the immobilizer or key fob might need attention. If you need any further advice or want help finding a trusted RepairPal shop in your area, please feel free to call us at 877-913-1554!