1989 Cub Cadet No Start

I'm new here, how y'all doin'?
So my 1989 Cub clicks the solenoid and that's all. I've checked a few posts on here and watched some of "Tyrell fixes all" videos on Youtube. I still can't get her to crank with the key, so I'm hoping you good people can help me out.
The engine is a Kohler Command 12.5 Hp. Mower is a 5 speed, not a hydro.
Here's what I've been doing:
Checked my grounds. I took the neg battery cable off the machine and sanded it down to bare metal where it connects. Sanded the battery terminal end as well. Sanded the positive cable too, both ends.
I changed out the solenoid for a new one, 4 post. I also put a 3 post one on that was on my parts mower. Sanded the paint off where it bolts to the machine so it'd ground ok.
Charged up the battery. It's 6 years old but I keep it on a battery tender when I'm not mowing for long periods, 12.79 volts today.
Took Tyrell's advice and tested the starter by removing the battery, ran jumper cables from it to a freshly sanded frame bolt and touched the positive end to the starter post. She wound over no problem; so the starter is good and the engine isn't seized. Pic below of starter and the shiny bolt below left of the starter.
Took off the ignition switch and cleaned up the posts. I put the ignition switch from my parts mower on; nothing changed (my parts mower is also a 1989 Cub Cadet). Pic below.
Took off the foot safety switch and checked it with my test light like Tyrell does. Normally open one side and normally closed on the other side. When you push the switch with the test light connected the test light goes on/off like it should. The foot brake lever makes good contact with the switch when it's depressed. Pic below
There is a safety switch in back of the gear selector, looks like a reverse cutoff switch to me. I tested it with my light and it switches the light on/off when you cycle it. It only has 2 wires going to it and the mower has always mowed in reverse. Pic below.
The seat switch has never been connected in the 20 years I've owned this mower. It looks like it goes open when you sit on the seat and the two wire ends have always been loose. Pic below.
I can't find a PTO safety switch anywhere. The gas tank is out and the deck is off, so I have good access. It's the old style lever arm PTO, not an electric switch. Is the PTO safety one of the two circuits in the foot switch?
I'm running out of ideas. I'm kind of down to a faulty wire somewhere? Maybe the current isn't getting to the starter with enough voltage (I can't hold the probes on the battery and the starter post and crank the key with only two hands, but I'll find a helper today). Or maybe a wire is worn through somewhere?
Any help is much appreciated...