Old thread, but I'm having this issue and I am fairly certain that the solenoid is not the issue.
Story goes:
I burnt out one starter because the signal wire post was broken and contacting the power wire. The replacement starter was brand new and cranked over once then made a horrible screeching noise and wouldn't crank again. I then changed the fender solenoid even though I didn't really suspect it was bad. It still didn't crank, so I had the starter warrantied. The new, NEW starter won't disengage. I crank, fire, then the starter is still cranking the whole time it's running and stops when I shut the key off.
I tried the new new starter on both solenoids, to the same result. I checked the S terminal and it checked out so that rules out the ignition (which is only 2 years old). Both positive and negative battery cables are brand new, as well as the battery.
P.S. 4.0L 5spd