Yeesh...that's a strange situation, nevermind the air pump's weird configuration! I'd probably look for a vacuum schematic at a library with Mitchell's CDs, which are basically very detailed repair manuals. They almost always have both vacuum and electrical schematics for every car they cover.
As for the purge solenoid, AFAIK (or at least on most Fords I've worked on), one end should go to manifold vacuum and the other to the canister. This way, the computer can dictate when the right time for purge is to occur. Note that this is the PURGE solenoid I'm referring to, NOT the TAB/TAD solenoids. They are fundamentally different in function and form. The purge solenoid is larger and has a metal container, with a two-wire pigtail coming out of the end, at least on most of them. TAB/TAD solenoids have a venting function when they're not energized. See if you can't find the TAB around the EGR control solenoid. That's where they are on Mustangs, at least.
Not that it's not possible, but I've never encountered a system with no atmospheric dump valve. You're getting a code for a TAB, so that indicates that the computer is anticipating one being there. If there is a connector for it, there definitely should be a TAB solenoid. However, I'd be curious to see if the computer in the car is the correct one for your particular vehicle. Ford made quite a few different computer configurations for same-model cars. Most of it depended on where it was to be sold, parts availability, for Federal/CA emissions standards changing, etc.
It's possible someone before you (as you indicated) has tried changing things out until it worked. As per the usual hillbilly-techno-know-how-or-not, the computer is always the problem.
I wouldn't be surprised if it was changed out with a junkyard unit off of the same model and/or year, but not of the same part number. I've encountered this quite a few times, unfortunately, and slight changes in the electronics configuration aren't going to work with a different system. Just be thankful it's not a Chrysler, they're a nightmare when this issue comes up.
Back to your problems, that two-foot loop going around and coming right back to where it came from is doodoo. Ford wouldn't ever do anything like that (oh God, I would hope not!), so that's a sure indication it's been messed up by someone. Yeehaw. As I said before, a vacuum schematic is going to be a great asset to figuring out where everything is supposed to be. Now that I think about it, it's possible that the dump valve is actually an integral part of that piece with the nipples on it. Therefore, something was attached to those nipples that controlled the dump valve....okay, I'm just speculating and I'm probably dead wrong. Upon closer inspection, it appears that the nipples are just tapped into the pressurized outlet on the air pump. A peculiar setup, indeed. On that note, I wish you luck.
Also, I'm moving this to the Windsor Power Forum. You'll get more responses in there, hopefully.