TO20 not starting

Hey everybody - I am racking my mind here and need some help. A friend of mine brought his tractor to me because his nephew messed around with the electrical and timing and screwed things up royally. I took things back to basics, disconnected everything and have just the engine electrical system hooked up, no gauges or lights at this point. The engine now turns over (which is was not before) but she is not starting. I replaced the coil, resistor, and it has an electronic ignition (note: this is a 12v system). Took the spark plugs out, put to ground, can see a spark but that doesnt necessarily mean I am getting a spark under compression. Fuel seems to be good. Maybe timing is out? Please point me in a direction lol

You say the nephew messed with the electrical and timing. The first basic step before any parts replacement to me would be to check that the timing is close, and the plug wires are in the right place in the distributor.

Bring #1 cylinder to TDC on its compression stroke and see if the rotor is pointing at the contact for the wire going to #1 in the cap. If not, you need to move the wires so #1 wire is where the rotor is pointing (Even if there is a post marked #1 on the cap, it doesn't need to be on that post, it needs to match the rotor.) If the rotor is between posts, he may have loosened and turned the distributor body. You may need to turn it some to align the contact and rotor if he did turn it. Not trying to underestimate you, but do you know how to establish that #1 is on the compression stroke? Just lining up timing marks only has a 50/50 chance of being right. If you aren't sure, ask and it can be explained for you.

Next check that the plug wires are in the proper holes in the cap, starting at #1 (which you checked/established above) by the firing order in the rotation the rotor turns. Firing order is 1-3-4-2, counterclockwise

Yeah I am suspecting it is probably timing - for TDC, remove #1 spark plug, put your thumb over the hole and feel for it to push your thumb away. I am then
verifying through the timing port under the starter and with a borescope through the sparkplug hole.

I will mess around with the distributor this afternoon and check everything you mentioned.

That is the way. I usually turn it by hand, once it starts to push my finger away, so I don't go by the timing mark, Easy to go by trying to do it all with the starter. Always turn the way the starter turns the engine to keep any gear slack in the right direction.

ok - Here is where I am with this one. I have 3 starters (original, replacement a few years ago, and a new chinesium one from YT), new coil, new plugs, new
cables, new solenoid, new ignition switch, and new battery. When I have the starter installed, the solenoid will give the open click, I am getting 12.6v down to
the starter, but it is not cranking. It act like it just does not have enough umph to turn the motor. If I pull the starter out, it will spin just fine. The
engine was turning a couple of days ago when I was trying to fix what my friend's nephew did when it came to timing when it wouldn't fire up.

Something else that is kind of interesting - when I turn the key and the solenoid clicks and sends that 12.6v down to the starter, I let off, and I ran a
continuty test between positive and the chasis, and I was getting continutiy. I disconnect the battery, and reconnect it, and that continuity between positive
and negative is gone. So with that, new cables all the way around and took everything else out of the equation. All I have hooked up is the coil, distributor
(digital), starter, battery, ignition switch, resistor (new), and solenoid - everything else is disconnected; even the alternator.

Any ideas? Thank you in advance.

The tractor has been converted to 12 volts, correct? Conversions can make it hard to give good answers as we can't see exactly what was done as far as circuitry in the conversion. You will need to be detailed and specific in details in describing circuits.

I believe the original starting system used the heavy mechanical start switch, not a solenoid. Apparently, this now has an electrically operated solenoid from your description, correct? What is it for a solenoid (do you have a brand and part number)? Many solenoids may look alike but are different internally. Is it wired only through the ignition switch or is the original starter switch still in the circuit? Where is the battery ground cable connected?
You can have voltage showing at the solenoid but not have amperage enough to power the starter. What does your voltmeter read at the solenoid when you try to start it?

Guessing it is now negative ground and if the solenoid looks like a Ford type. Unhook the cable going to the starter from the solenoid. Make sure the tractor is in neutral. Hook the red cable of a heavy set of booster cables to the battery positive. Use the other end of the red cable to apply power to the starter cable you removed from the solenoid. That should make the starter turn. If it turns the problem is from the solenoid back. If it doesn't turn, try using the booster cable to apply power direct to the starter stud. If it turns then the cable between the solenoid and starter is suspect.