Ell I hate to tell you this, but just about anything that is electrical could and most likely is shot! Check, and replace all fuses to start with. But I bet you will need to replace all electrical parts on the car. Take the major ones in to your local Car parts place and have them checked out free. Like the Alt, coil, distributor, and such. Possible the Ignition, and fule injection system and such. ANythign that gets power is shot. Possible even teh battery got damaged.
Now you will also want to replace your terminal wires, and make sure to get a RED one for the positive side so that this does not happen again. As it is a costly mistake. Good luck with it. I have had many mustangs and I love them. 65 cpe, 68 FB 2+2, 85 sedan (ex cop car), & 95 svt
cobra. I miss having a mustang, but as a single dad to 5 boys its just not practical. But at least I get to shoot a few of them in my line of work. Check out my website to see what I mean. Have a great one.