Please help, The whole electrical system shut down on my cay. Nothing is working other than a blinking car with a lock on it on the dash. What can I do?

 

battery might be dead, or a battery cable
may have come loose. also one or more fuses
may have blown.

 

If it is your original battery, I would suspect that it is dead; probably a dead cell. Battery is nearly always the first thing I had to replace on some 15 new cars. Look for corrosion on battery cables, perhaps it is something simple. Might be a main blown fuse, but I am not sure if the Mustang uses those. Good luck, and hope you get it fixed soon.