1973 Cougar doesn't shut off when key is turned
 

New to the forum as I've tried a few things to no avail.

I took my 1973 Cougar out the other day for a quick drive and on the way home it started sputtering as if I was getting vapor lock on a 70 degree day. I let it cool down and started it again and when I went to shut it off, the engine kept running. The battery is now dead and jumper cables get immediately hot if I try to charge battery. I've changed the ignition switch, starter solenoid and banged on the starter with a hammer. Any other thoughts on what I can do to fix this?

Thanks!