340 Engine Shake

That's a lot of double speak man. No offense meant.

"Not 100% sure" followed closely by "but it's isolated from the ignition".

It's this kinda thinkin that can lead to you forever chasing your tail. VERIFY it. Don't just assume. You obviously have SOMETHING GOING ON SOMEWHERE and this kinda talk and attitude ain't gonna find it. You need to have an open mind to every possibility, or it'll end up someone else's project car when you've had enough.

You're right. I can trace back to where they plug in and unplug them and see if anything changes.