Only Cub Cadets - lost on this electrical :(

back in june I had my 122 running after being restored, not to long after I was pretty sure I had a shot battery since I had taken it from a junk batter pile. I charged it up and it held charge for as long as it needed to. i tried charging it plenty of times with my only luck being a very slowly turning over, just recently i tried putting my truck battery on with no luck. today i tightened up all the wire connections and put the battery in, trying to put the battery terminals on with a bunch of sparks coming my way, once the sparks stopped there was smoke coming off of the voltage regulator in the dash and on back of the grille, maybe somewhere else to. i then put the old battery back on and put the charger on and the alligator clips started to smoke! i am lost as to what my real problem is and would appreciate helpmuch because i was really looking forward to pulling at the fair on Friday night since it is the last one. Please give me some guidance