Another 870 thread- Engine vibration

[ZeroNthedark]

==Well, I'm pretty stuck, so figured it was high time to dust this off and see what happens==

I won't bore anyone with mundane details yet, so the short version is thus-

Finally had no choice but to order a new harness. Had tried to do some troubleshooting by replacing wires that were obviously in terrible shape, just to see what did and didn't work. Truck had gotten so bad it was actually activating 3rd stage of engine brake randomly at idle, amongst other issues. Got it overnighted, installed today and now the truck will not start. Won't even try to fire. And I drove it home before taking old harness off.

Triple checked all connections and everything "looks" good. The harness fuse is good, besides being brand new. No bent or broken pins in ECM.

Tomorrow is another day, but until then any ideas are greatly appreciated.