well, I would love to show more details, but this ought to suffice for someone who digs into this:
long story short, make this thing:
... also I have no idea if this is NASA-grade or if there's any consequence to it : 18 gauge copper wire (the bundled kind... not a single piece), spade connectors from a small box from the FLAPS - one as-is, the other I had to simply file down to fit. when I did this, I discovered the tip is made from metal that is folded over on itself. In between was a yellow tint. No idea what that is. Moving on - crimp it, forget to put shrink tubing on it so I used a huge shrink tube, used about five or six different tools from the bin, and voila - when you plug the ends in as shown - the side with the normal size spade is to the radio wire harness blue-and-nothing-but-blue wire, the other side is the shaved spade to fit into the power antenna power wire (so awkward to describe this for a novice) - ... it is very obvious when you plug it in. The station reception goes from OK to a little better than OK, but when you scan around for stations, it is obvious. AM - well, haven't tried yet. the smartphone radio transmitter unfortunately doesn't work much better... meh, maybe a tad... press one of these buttons... oh neat.... next, I took the same 18 gauge copper wire and ran it from the little connector near the battery all the way up and over and down to the fuse box. This might have helped a little - perhaps 777 can say if the 18 gauge copper bundle wire is a dumb idea or not...
BUT
... that's it. oh also '87 944 NA - looks a bit different. the detached wire goes to one of those stiff black wrapped bundles and curls around somewhere, maybe the remaining Blaupunkt wire harness, ... actually might have that manual somewhere... there's other mess in there but I call it done after a bit of electrical tape on the ends.
FM radio - it is a glorious time to be alive.