Arcing at the coil - input?

2000 Mercruiser 350 MAG MPI on Vdrive
Pulled rider today about 20 minutes, then when idling to switch out rider, engine started to run rough and stopped, would not restart with repeated tries. Started paddling toward shore (fun fun fun)and after about 15 minutes, tried starter again and ran like a champ. Zipped around lake a few times but when we got back to lift, it starting running rough again. Looked over the engine for a few minutes before seeing arc at the coil. The coil has center wire to distributor cap, and two smaller wires, one left, one right side. Arc was going between left side wire and center. I stopped engine right away and when I moved center wire, it came right off leaving connector behind and looked slightly burnt/crusty(?) inside. Any input on if this requires a new coil or just wires, or bigger issue causing?

Sounds like it's just the wires. If that ones bad others are probably too. Just get a replacement set.

Razzman's got it exactly. It arcs from the center 40kv to the ground on the field. You might want to change the rotor just to finish possible problems, and clean any carbon tracks from the top of the coil.

Go a head and replace the cap also.

Any need or method to test the coil itself? I plan on following the feedback and replacing wire set, cap and rotor, but have never had a open spark in the engine compartment (and hopefully never again) and want to cover the bases.

The coil works, obviously. but if you want to see if it still arcs just watch it with the hatch up when you start it at night. Inspect it for cracks and carbon tracks from the past arcing. I doubt you'll find any cracks near the terminal and you can clean carbon track off. The new wire and boot should fix the problem.

We know it works, hence the arching. The spark is looking for ground and will take the path of least resistance. Right now, that is the bad wire. You can Ohm the coil from the 2 primary terminals to the secondary post. Those coils are pretty tough though.

Before I read your post but after I saw the title the first thing I thought of was a bad coil wire from the coil to distributor. After reading your post that is clearly the cause.

Like water, electricity follows the path of least resistance. As spark plug wires age and dry out and harden the resistance increases dramatically. I've seen several cases of coil wires being so bad that the coil starts arcing to the nearest ground rather than through the wire, which is what happened for you.

If the coil wire came off in your hand it's shot, change it and the cap and rotor because you clearly haven't changed either in a long time. Coil is fine.

keep that blower going...