Can I use a soleniod from a Ford truck in a Ford 9N tractor?

Answer 1

Assuming that they are both the same generic age and both 6v, there is no reason that you cannot use it.
--Are you talking about the solenoid that is built onto a starter, or the small remote solenoid that is often used?
Ford 9N tractors were built with 6v systems.
If the Ford truck solenoid is newer and 12v, it may not work with your 6v battery as some equipment is voltage sensitive; and if it does work at all, it may burn out more quickly.
Have you converted the tractor to a 12v battery? If so, the 12v solenoid will work perfectly.
Remember that six volt ( 6v ) equipment is by it's very nature wired with heavier wire because it is required to carry a higher current at the lower voltage.
For instance, you can use a 12V battery to operate a 6v system in a tractor, it will start the tractor and the 'generator' will even charge the battery however inefficiently, -- but the 12v will quickly burn out the LIGHTS if they are still 6v. bulbs. The rest of the equipment will operate just fine because it is wired with heavier wire.

Answer 2

If you already have one, give it a try and find out.