Well I feel like an idiot. I'm guessing the missing relay circled in the pic is the main relay. The one that was very corroded and nasty, and I have to get channel locks on to pry out.
After looking at the circuit diagrams from the BGB, that and a blown fusable link on the Head unit line (Line B) would explain 99% of what doesn't work on the car. The 3v was coming from the fact that the last owner had connected the lines by the dizzy wrong (what's the clear one for? That was powering the coil). With green to green (or gray in my case), I'm getting no power, just like it should with the main relay out.
Also, for the benefit of those of use without diagrams on the fuse box lids, are they out there on this site?