I'll set the scene:
Had an old battery in my 98 XJ that couldn't hold a charge, received brand new battery and attempt to install it into place. Accidentally connected the wrong ends (I know, stupid). Que smoke, arcing electricity, and the car horn starts going off before all goes quiet. Kicked the tires and left it for another day.
Next day, flipped the battery around, connected positive, everything is fine. Used a multimeter to check the battery to make sure I didn't somehow kill it, everything seems fine. Connect the negative end, sparks go off and smoke starts to come out of the front of the alternator along with a whining noise (probably it's death rattle at this point). None of the wires felt warm and no wire damage can be found. Has anyone had this happen to them, or do any of you have an idea as to what I should do next?

 

To the best of my knowledge, connecting the alternator with reverse polarity will destroy it

The smoke was the internal diodes

did this once myself...although in my case, it was a super weird situation...found out a new thing...a dead flat battery, will allow a battery charger to be connected with the wrong polarity, take a reverse charge, and you will be none the wiser...until you hook it up and fry things

 

Yep. Once you let out the magic smoke, those diodes are a dead short, so when you hook up again...... Not pretty.

 

Its dead, Jim.