John deere

Not to get ticky but I just caught the 66 model. If it's a 66 it has to be a 5010. The 20's were 68 to 72 I thought

 

Not sure on the 5010's,never had anything near that big around here,had a 4010 diesel once.I know they were over in 1964.4020's were 65 to 72.
Just looked up Tractor Data,they say 65-72 also for the 5020's.They've been wrong before though.

 

I have been wrong myself lol

 

Who owns the tractor. If it don't run, let them pay the charges to off ld it at the port. Not the haulers responsible for mech issues. Yes I do all I can to help, but not wasteing my money and time on a bad unit, I don't own

 

passingthru has the deal!
But to explain the the likely cause you do not understand this is the problem. The solenoid is an electro magnet. It pulls a piston through a cylinder. One end is connected to a lever that pushes the starter drive gear into the flywheel. The other end is a large contact that connects the two large terminals on the end of the solenoid. One goes to the battery and the other to the starter motor. If for any reason the power to the solenoid is low movement can be slow allowing the contacts to arc and weld together on contact. Yes the drive can stick but it is usually the contacts and can happen on a brand new unit with bad batteries. Some types hang with the drive engaged and others without. If it happens on your truck it with spin the engine until something burns up or you get the cables off.
NM you are correct the ground circuit of the starter is not connected to the block and there is an extra terminal on the stater for one of the batteries.

 

We had a 6030 pulling tractor that would shear the bottom shaft in the transmission, which doubles as the pinion. Had a lot of fun hauling that thing around