So I just ran into something interesting while looking up different scenarios for your situation. I know we mentioned the ballast resistor and how we're pretty sure that it's ok, but I'm on RockAuto's site and checked the ballast resistor basically just because I was curious how much it cost and it came back with this:
That's not what I was expecting to see when it's listed as a resistor! But those ends look awfully familiar when compared to mystery wire #2......
So I went through ALL of the wiring diagrams in my Haynes manual and the only 2 places I found a black with yellow hash were on the rear window defrost circuit and the AC clutch circuit. I'm going to guess that mystery wire #2 is for the AC circuit, so it's not important to get the car running. But, if this wire goes to the ballast resistor circuit and you can readily identify it, it wouldn't be a bad idea to check it for corrosion and continuity, although I think we've pretty much ruled out a problem with that circuit.
I also opened the first page of the ignition chapter in my Haynes manual and found that the coil is only rated at 8v and the ballast is 1.5 ohms. And I said something about checking the clearance for the pickup coil to see if it's something like .015"-.030" - that is not adjustable as designed and is checked by a voltage drop, so the previous test I shared is probably the way to go in that case.
So, since the coil is rated at 8v, the 8v measurement you noticed earlier is what it's supposed to read which means that that circuit is apparently working.
You mentioned that you checked the pickup coil but weren't 100% sure you checked it correctly since it's a 3 wire connector - you'll connect the leads of the meter to the same color coming from the pickup. In the pic of the one I'm looking at on RockAuto it would be the purple and orange(?) wires.