I was asked about my solenoid installation, which was part of my battery cable replacement, so I thought I'd add the info here, to complete the picture.
Here's the OEM installation for reference:
The small "extra" red wire was indeed a take-off from the positive battery terminal. I decided to crimp it into the new positive battery cable at the solenoid, which lives under the seat of my 2011 B5. The following pic is the new installation; the arrow shows the connector which has the battery cable and the small red wire crimped.
Sorry it's not shown well, but that small red wire is in there.
The heavier wire that crosses the top of the solenoid is the negative wire of my Battery Tender lead. The terminal end with the red collar is the positive wire of the Battery Tender lead. It's kind of hiding the + battery cable, which loops down and back up to the + battery terminal. The Solenoid terminal without the arrow is the positive lead which runs to the starter. The two small pink spade connectors are the leads (small blue and small white wire) which activate the solenoid through the handlebar starter switch.
For installation, I cut the old wires which were bedded into the OEM solenoid (getting rid of them all anyway) and removed it from the bike - two bolts hold it to the frame by a U-shaped bracket which is lightly tack-welded to the solenoid. I clamped the solenoid lightly into a vice, and using a flat screwdriver as a lever, I tapped the U-bracket and it popped right off the solenoid.
The new solenoid fits the U-bracket almost perfectly. Since I didn't have a way of tacking them together, I wrapped a couple layers of friction tape around the body of the new solenoid (you can see it in the pic above), and wedged it into the bracket. I checked out some copper pipe hanger (the metal strips with holes that plumbers use to hang pipe from basement overheads) and found the holes lined up nicely, so I cut a short section to hold it in place from the top. I wedged a strip of compressible closed-cell foam in there for good gripping pressure. Another bad pic: