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I have the above engine (Spec No. KT745-3066, 2016 mfg date, 270hrs) that's giving me issues. The problem first showed up as a loss of power; after inspecting spark plugs, I realized it was only running on one cylinder. New plug and coil later, still no spark. If I remove the white wire that plugs into the coil (I've heard it called a ground, and a 'kill wire'...idk what it is, honestly) I have spark, and engine runs correctly...full power, blades, everything.

Separate issue (but I believe must be connected): engine will not start at all, unless choke is applied...in which case, it fires right up, just as it's supposed to.

Also, not sure if it makes any difference in terms of diagnostics, but the engine is powering a 2016 Craftsman G8400 ride-on tractor.

Really, I'm just stumped at this point. Any help would be appreciated!

Replace the working coil as it is the root cause of the other coil not working..

Your kill wire, white wire, is shorting out. You are going to have to trace that wire back to the key switch, looking for an insuati fray where the wire is touching metal. I wouldn’t worry about the choke, as it is working properly, just a little annoying to choke a warm engine.

Have to respectively disagree on this as I already had this problem twice this year and both times it was the working coil.

No point trying to explain why.

The kill wires are connected to each other .
As such if one sends a signal down the wire it will affect the other .
When this was discovered they put a diode in the wire between the two coils.
This was easy to diagnose & fix .
Then when the new coil design was made the diode function was added to the Hall effect trigger chip embedded in the coil
So when when it fails you have to replace the entire coil not just the 50¢ diode .

I was wondering if the original coil that was still functioning was causing something amiss, considering that the 'leg' running to the new coil comes from the old one.

I do feel comfortable ruling out wiring damage, as the whole harness (at least the portions that are easily visible) look new...other than being dusty. Haha!

Thank you all for the help! I will replace the other coil and go from there.

The standard test is to remove the kill wire all together.
Then disconnect them one at a time
It is what Star was trying to tell you.