Hello everyone,
I've got a 1940 9n it has 12 volt conversion 8 years ago with electronic ignition that won't start. I was using tractor leveling some dirt shut it off and came back about 1 hr later and it wouldn't start. It turned over Very slow and the negative battery cable got hot and started to smoke. I took battery out to charge battery as I left the key on cleaned negative cable on both ends to make sure I'm getting a good ground. When I tried to start tractor the negative cable got real hot again and wouldn't turn over. Does anyone have any suggestions???

there is corrosion under the crimped lug on the battery cable that you cant see unless you cut it off. corroded /dirty/loose connections cause heat. some auto/battery stores can repair or provide a new copper lug and a loan a tool to crimp it back on.

Are you saying the starter won't crank the engine or the engine fails to start with good cranking ability of the starter?

It's sounds to me from your description your starter has issues and is pulling a lot of current. I would atleast start by cleaning all battery, engine ground and starter connections.I would have the battery tested just to rule that out before proceeding to the starter.

Larry,
Your battery may have a dead short internally. Does the battery hold 12.6 volts when fully charged?

I suspect if the battery was internally shorted, it would be dead or just explode nicely. Your problem is an internally shorted starter.
Tie the tractor to the back of the mini van and have the wife drag you around a short distance. It should start with no problem. Turn on the key to run position, and in 3rd gear. Turn the key to start and the cable warms up due to dead starter.
Capeech?