Starter wouldnt stop spinning...?

Upon trying to crank my 96 4.0 tonight, it started to turn over, but not long enough for it to fire up, and I noticed the starter was just spinning and spinning, even after turning off the ignition. Had to disconnect the battery. I could smell the starter by the time I disconnected the battery so Im sure Ill need a new one. What caused it to do this? Ignition switch?

Help please asap, this thing is stranded up at my work.

Sounds like it is not "actuating" ? I can't remember the word for it.. basically it's not throwing the shaft forward to engage in the flex plate.. and.. I think the solenoid would be the culprit?

The catch is, the darn thing wouldnt stop spinning without me disconnecting the battery.

The bendix is rotation-speed-actuated, and is spring-loaded.

What you describe is either a faulty bendix, or insufficient battery power to fully actuate the bendix, thus permitting the shaft to spin freely vs. engaging the flywheel and cranking the engine.

(If it were the solenoid, no power would be getting to the starter.... Typically, at least. I suppose a partial-throughput failure COULD occur, but it isn't common, I don't believe. It tends to be an all-or-nothing part, functionally.)

as i had my starter out yesterday in my 98 ill say that the solenoid could have possibly hung up once it pulled in theres a spring in there could be weak or broken perhaps dirt could be in the solenoid making it drag bottom line pull the starter and disassemble the solenoid off the side of it and take a look i guess now that i think about it you should put a meter on the wireing b4 you pull the starter. if you have
the power dist box under the hood and u should since i see its a 96 pull the relay for the starter and check for 12v while someone turns the key do it multiple times cuz if its the ign sw. it might not act up right away if i remember correctly the term you want to read for voltage are the 2 that are faceing the front of the bumper and the rearmost facing the windshield hope that helps i guess its worth mentioning the relay could be sticking too swap it with one of the other ones that gets less use maybe the a/c or one of the other ones good luck

if it kept spinning after you turned the key off, either the ignition switch has failed and is still sending electricity to the starter relay, or the starter relay has failed and stuck in the closed position sending power to the starter. Low battery voltage or a poor ground circuit can overheat the relay contact points and cause them to stick closed-- it's not the only way to cause the problem, but worth checking before you replace the relay and do it again.

I'm assuming you haven't been under the vehicle messing with anything that could have caused the small wire in the starter to contact the big cable on it, but you may want to check that out too.