No go

I think you meant 'assume positive ground'.

Otherwise.. ya.. what you said.

Soundguy

If you have an 8n with the stock starter button, you can simply ground that small wire coming off the starter switch.. be careful... this bypasses the neutral cutout... that will trigger the solenoid.. if it doesn't.. check that your battery is charged ( did you leave the lights on a week ago? )

Anyway.. if the battery is charged, and grounding the wire doesn't do it, try jumping around the big starter solenoid... if noting there, my guess is something is open or stuck in the starter.. sometimes if it is stuck, or just starting to go, a small whack with a hammer while holding the start switch will free it up.. ( a small whack.. don't cave the side of the starter in.. )

As a remote possibility, the starter drive may be engaged and stuck in the flywheel... If it is, usually vigorously rocking the tractor back and forth by grasping the rear tire, in 4th gear will free it.

let us know what you find out... ( be sure to check the battery voltage.. and also check the voltage while depressing the start switch.. might just be a weak charge on the battery that drops to nothing under a load )

Soundguy

The first thing I would check is the battery. (If a battery is on its last leg, a change in the weather like a heat wave or a cold wave will finish it off). Next, I would check the connections, solenoid and starter switch. HTH. Rick H. Ga.