I will venture to say you have a defect in the key switch, or the wiring that serves the key switch. I lean strongly toward the key switch because you have a problem with both cranking, and killing, the engine.......in the normal way.
The cranking and the killing only have one common component wherein a defect would affect both, that would be the ignition key switch, or the terminal connector block that plugs to the key switch.
Some OEMs converge the safety interlock kill wires at the engine makers kill wire terminal on the engine. If the wiring is configured that way, a defective key switch would not kill the engine, but the seat switch interlock would kill the engine.
Some OEMs converge all the kill wires and interlocks back to the key switch. If the wiring is configured that way, a defective key switch WILL NOT kill the engine and the interlock kill circuit is also disabled.

This sounds like you.

Mownie first let me say I have read so many of your previous post that I feel like I know you. Tk you for all that you do to help folks here!
Key switch was my first thought on the first wiring harness. I then bought another complete harness with key switch, pto, solenoid, and trans. connector. The second harness was a little different because it does not have a headlight circuit. But I still have the same problem.
I will try to get another key switch to match the orig one and start over with the first harness. Tks again.
Dayton

pch, you have my full attention.
If the next harness/switch combo does not make this horse behave, let's try some individual tests to see if we can I.D. the issue using the original harness and switches. I have no problem with folks using "known good" salvaged parts to diagnose problems, but I tend to cringe when new parts are lobbed at a machine as the first approach.
But then.......I've heard stories of that being how some so-called pro shops diagnose things (but using the customer's money, of course).

The second harness was used also. Thought I might luck out. It may take me a day or two to make it up to the big town for the switch. But it is over 100 degrees here right now. Been that way for over two weeks. I'll check back when I get the starting harness on with a new switch I hope. Have a good day.

Well, don't feel like the Lone Ranger, thermally speaking that is. Here in middle Tennessee, I think I heard one of the TV weather personalities say that we have gone for over 45 days now where the high for the day was over 90 degrees. For the last three weeks or so, we have had daily heat advisories and folks just to our west have had "Excessive Heat Warnings" daily.
A lot of towns around have had highs of 100 + with "heat indices" of as high as 118 (wrap arms around air conditioner and swear your undying love for it!).

"Mownie first let me say I have read so many of your previous post that I feel like I know you. Tk you for all that you do to help folks here! "

Now you've done it.

Walt Conner

Oh yeah, I forgot to say I been reading Walt's post also. I think they may be co-authors of a shade tree mechanic's book.

HA! Walt would say I write a book with every post.
He would also admit that he has never read one of my "books" from start to finish (well, at least not without a couple of naps in there somewhere). :^)

Got my problem solved. It was not the magneto as I thought. I put the orig harness and starter stitch on after cleaning all connectors and posts. Tried it and solenoid clicked. I put another solenoid on and it cranks...runs....and cuts off with key. Must have been a bad ground or a wire that was kinked around somehow. So now if we can just get some cooler weather and a little rain. You two wouldn't happen to know how to do that would you?

Perseverence certainly pays off.
Regarding this problem of the starter control circuit not activating the starter solenoid. When a solenoid does not "kick in" when the key is turned to start, a good way to begin the search for a cause is to jumper from the BATTERY SIDE of the solenoid over to the small terminal on the solenoid to see if the solenoid will activate that way. If the battery is not dead, a good solenoid will activate using a jumper, and the starter will turn.
Caution! If your solenoid has 2 small terminals, DO NOT jumper to the grounded terminal.

Of course, the solenoid is a 12 volt DC component, and like all the other electric parts on a machine, it too requires a "hot" & a "ground" to function. Any tests of a solenoid should include confirming a ground as well as any checking done to the "hots".

I can't do anything at all about getting some rain, but I am working on a project to bring in some cooler weather. I expect to see some results about the first or second week in October. Write that down. :^)

Cool! My solenoid does have two small terminals. One goes (or comes from) a wire on the transaxle. The other one goes or comes from the PTO switch on the dash. Are those considered the safety switches? Only other safety is under the seat. Aren't we glad I got it going before we had to go into safety switches. I've seen the other discussions on those. Whew! Very had to fix over computer.

***"My solenoid does have two small terminals. One goes (or comes from) a wire on the transaxle. The other one goes or comes from the PTO switch on the dash."***
Those 2 switches comprise the "starter inhibit interlock" circuit.
The wire leading from the PTO switch to the solenoid is to inhibit the starter from engaging if the PTO switch has been left engaged. This way, the starter does not have to fight against the extra load of whatever PTO driven attachment is in place, plus, it addresses the safety consideration of preventing the attachment from becoming active when the key is turned to start.
Now, the other circuit that leads away to the transaxle, is connected to a "neutral safety switch", which will provide the starter solenoid with the necessary ground for it to operate,.....only if the trans is in neutral. That way, there is no way to start the engine with the tractor in gear (except bypassing the solenoid).

The seat switch function affects only the ignition spark by grounding the magneto (in this case).

After reading questions on these boards, it seems to be a common misconception that shorting across the two large terminals tests the solenoid.It only tests the starter motor and drive,the method called out by Mowie in his 15:53 post tests the solenoid.The method of trouble shooting he referred to is often called "shotgunning" or replace parts till it's fixed.I've seen people replace several parts without trying it out and don't know what fixed it when it works.Usually someone else's money.

You are soooooo correct dc3mech. That's why I've bookmarked and read with renewed enthusiasm the posts in this forum. While I never had a lot of mechanical or electrical education....what little I did have... added to what I read here might save me some money. And I enjoy tinkering. And besides, where else can you go to listen to gruuumpy ole men spreading such cheer and knowledge at the same time?