850 versatile died in field help

Sounds like you have a big short somewhere. Could be in key switch circuit

What type of shape is the alternator. The location of the versatile alternator often get plugged with dirt and straw and often the diodes burn out or other parts in the alternator get hot and burn out. I actually keep a spare alternator in the shop for my 946. Poor alternator would cause poor power to starter.

That should be a Series II. First place I would go is check the wiring related to and starter relay itself, this as mentioned already is on the front of cab. Most likely the relay is stuck or it is getting powered by a shorted source, which would have to occur after the start switch in the dash. The two small terminals on the top of relay, one goes to the starter switch, the other to the charge relay in the dash. The problem is that relay is most likely remaining activated either because it has continuous power or the relay itself is NFG. That relay is what activates the solenoid on the starter.

Also just thought I would add this, once a Cummins with the electric shut off on a PT pump drops to about 7 volts it will shut off the fuel simply due to low voltage. On another note, if ever needed, there is a screw you can turn in manually to override the electric shut off in emergencies to start or keep the engine running.

Yes it’s a series 11

 Had a similar problem this spring on my 4010. Started the tractor up to run a swing away auger and a while later I walked by the tractor and smelled burning wires. shut the tractor off but the starter was still engaged. had to run get a 1/2 inch wrench to disconnect the battery to stop it. tried reconnecting the battery cable and it wanted to stay engaged even with the key off so I had to leave it off. Brought the starter in thinking I needed a solenoid and get him to check the starter over but the starter was toast already, needed a rebuilt. I explained what happened at the shop and he said low batteries was the problem, the starter won't disengage if they are too low, they have enough juice to start it, but not to kick out. Sure enough after I put the new starter on and charged up the batteries I checked and the alternator was shot, not charging.
 If I were to guess I would say that when your neighbor started up the tractor the starter never did disengage while he was working, thus the super hot starter and burning wire smell. And unfortunately your starter might be toast too if it won't work with charged batteries. I would go get it checked out, and your alternator too, that is probably what caused the starter problems. good luck

There is something inherently wrong with this...for example on your 4010 same as with this Versatile, all the relays and solenoids  involved utilize electromagnetic force to over come mechanical spring force...if you try to operating them with low voltage, the relay or soleniod will not hold a closed position or will not close the contacts because the low voltage to the electromagnet is not strong enough to over come the spring pressure. There is no physical way that low voltage can cause a properly operating relay or starter soleniod to remain engaged or engage on its own, its mechanically impossible.

This is why like on an older Ford, when you have a low battery, you get that chattering from the starter relay/soleniod. Thats because momentarly there is enough voltage to engage the magnet inside the relay, but once the contacts close, the starter now draws which reduces the voltage causing the relay to open...this repeats rapidly under the right conditions, thus the chattering those old Fords were known for.
The only way a starter can engage while running or remain engaged, is if some other factors are at play as in faulty components ect. After the power is removed from the soleniod, the spring forces the contacts open and pulls the bendix from the flywheel, or depending on design of the bendix, the bendix is automatically thrown out of engagement of the flywheel when the flywheel begins to spin at a greater speed than the starter thru the function of an overrunning arrangment. The bendix is the gear drive assembly on the end of the starter that engages into the flywheel teeth.
There had to be something else at play in your situation with your 4010 or the guy telling you this didn't know what he was talking about or you got something crossed up. Now getting into computer controled crap, stupid things can start happening with low voltage absolutely, but not with a mechanical system like was in play here in both cases.

Also Versatile is all straight 12 volt other than perhaps the 1150 with the KTA, but to my knowledge it is only 12 as well.

Guys I personally have no idea how it works, honestly I am not good at all with electrical, I am just trying to tell you about my experience. All I know is the starter would not disengage. I took it off, brought it in, was told it was toast, took the rebuilt home (with a new solenoid on it), put it on, recharged the batteries and fired it up and it worked good. Checked the alternator and it wasn't working so replaced that too, haven't had a problem since. Maybe it was the solenoid on the starter that the low batteries damaged? I don't know. The biggest thing he stressed to me is keep my batteries charged good because low batteries reek havoc on starting systems.