Okay, just a little more info needed here. Am I correct in my belief that you are saying you have power to the fuse array under the dash? How were you able to determine that?
Further, as you say, when you turn the key, you get no response, not even a click, at the solenoid?
This, to me is still about the wiring. If there has been some serious fvckin' around done with the primary wires down at the solenoid as you have indicated, then has there been any damage done to the wire from the starter switch that actuates the solenoid when the key is turned? Are the copper ground straps that run from the engine to frame or firewall still in place? Have you done a pile check on the battery to learn if it can take and hold a charge? Has it spent any time on the charger or is it in about the same condition as when the car came home?
As an FYI, the engine bay harness is bi-polar. That is it has two major circuits, one which contains the wiring harness for the lights, turn signals, side markers, and horn(s) and the other which has the start and run wiring for the engine. Once you finish dissecting away all the sheet metal and plastic covers on the donor vehicle to get to the master connection on the firewall that I mentioned, you may actually find that you need both sides of that plugin. If you can pull if off, once you unscrew the center bolt or fastener that secures that plug assembly to the firewall socket, take the whole thing. The two halves are independent of each other but sit in a common frame or retainer. As a while you're there, grab the nuts and bolts and screws that you had to remove or unbolt or unclip and bring them with. They tend to be the small parts that you will find yourself without when you need them the most.
As for the harness swap, you can access that firewall socket by removing the driver's side front wheel; jack stand or block the frame here, and then carefully removing all the screws that hold the inner wheel housing in place and removing it. There are a lot of them, they can hide under dirt and crud, and they have two head sizes, 13mm and 10mm; yeah metric. 13mm roughly corresponds to 1/2 inch, 10 is unique and means a trip to O'Reillys or Napa or ? to get the correct socket or wrench if you don't have it. if a fastener won't budge, penetrating oil is your friend. Warning!! Do Not use heat on a fastener that has been sprayed with pen-oil, some the chemicals are toxic when exposed to heat!!! If the fastener moves but then gets hard to move, don't try to force it. You can try to "encourage" it by rocking it back and forth/loose and tight, to see if what is binding the threads will drop away and allow the bolt or screw to continue to come out. if it won't cooperated then get it back to where it is loose and spray it with P-oil, wait a little and try to rock it again. Lather, Rinse, Repeat. The fasteners may come out easily or they may fight you every turn of the way. PATIENCE.
Ya gots questions?? Ask. Only stupid question is the one that doesn't get asked. (Although there are quite a few that should have had second thoughts attached to them before getting said aloud but that is another topic for another forum altogether)