Ignition switch issue

I have a 1995 Pontiac Grand Am that ran
great for 1 month or more and then oneday
it would turn over but not start. This problem
went on for quite sometime.  Put it in the
shop for almost 2 weeks and even the
mechanic couldn't figure it out. Told us to
come get it and didn't charge us a dime even
for the shop time. Well my husband and his
buddy stumbled across the problem. It was
the ignition switch.  Replaced it and it
started acting crazy a few weeks later. My
husband has replaced the fuel filter, air filter,
fixed the catalytic converter, cleaned the
mufflers and all out. Put expensive injector
cleaner in it and still it's spitting and
sputtering like crazy!!! It's like it will go and
wanna run wide open and then once it gets
warm it's a retarded car!!! And it's got one
heck of a motor in it and it likes to go fast.
Well when he drove it up the road today he
said he could smell the ignition switch
getting hot again so long story just getting
longer he traced some wires back and 3 of
them were good and the other one was solid
black burnt!!! What in the heck is causing
this wire to ground out? ?? I'm sorry it took
me so long to get to the point but I had to
give some back story...