First time post. I have a 2008 Mustang V-6 with automatic transmission. Parked it last night and in the morning would not crank. With the key out the security light is flashing. With key in and in the ON position it stops flashing. When I turn the key I can hear a clicking in passenger kick panel. Battery is fully charged. Lights work, horn works, radio works, windows work. I've tried swapping starter relay with horn relay. I'm stumped. Any help would be appreciated.