Well, let me state the obvious and risk sounding like a jackass, but something's not right. (This is where you say, "No sh*t, Sherlock.")

I still think you have a floating ground somewhere, but the current surge caused when you inadvertently touched several wires might have cooked a diode or some other part on the cluster PCB.

Finding a spare cluster is an excellent idea, both as a diagnostic and to have for emergencies. Remember that if the replacement works and you decide to use it, you can transplant your speedo head into it and preserve your indicate mileage.
--
Don Foster (near Cape Cod, MA)