98 Blazer starter won't stop "CRANKING"

[Stratus SE+]

I'm new here ........hope someone can help me!

My son stopped by the other day and when he backed out of driveway his 98Blazer 4.3 quit,when we opened the hood one of the alternator wires was burnt (fusable link).
I replaced it,he drove home and the next morning when he tried to start it,it would not stop CRANKING OVER.
we checked the wire and replaced it ,he replaced the ignition switch,we checked for cut,burned wires,nothing.
replaced the starter and the same thing,when you hook up the battery cable it starts cranking over with the key turned off.

Any suggestions?

[BlazerLT]

Ignition switch or the ignition key tumbler is bad.

[cobash]

also check the solenoid on the starter it might be stuck as well.