Here is the followup article to my earlier one on the Videx 80 card and softswitch. We'll go step by step through the process of making the legendary One-Wire Shift Key Mod for Apple II. Then you'll earn your merit badge just like I did last week! 
The basics: What is the shift key mod and why do we need it?
Do you have a mostly-stock Apple II Plus or integer Apple II? What happens when you press the shift key? Can you detect a shift key press from an assembly or BASIC program?
Most likely the answer is no because pressing the Shift key closes a circuit only within the keyboard and nowhere else is this state relayed to the Apple II.
Because the first Apple II models shipped with an uppercase only keyboard and display screen, authors of word processing programs needed a work-around to know which letters should be capitalized and which should be lowercase. They'd typically show uppercase in INVERSE style, and lowercase would be the usual white-on-black display, but all characters on the screen would otherwise be uppercase.
With the shift-key mod, you connect a single wire from the keyboard encoder to SW2 on the Game I/O port. Then you can read the status of the shift key by looking at $C063 which is a generally-unused push button input (your typical set of paddles or joystick for Apple II used only SW0 and SW1 pushbutton inputs).
If you have a Videx Videoterm 80 or a similar 80-columns card, the firmware onboard is also made to detect a press of the Shift key via the single-wire shift key mod. So if you have an 80-columns board and have not made the single-wire shift key mod yet, there's no good reason not to.
What you'll need
The absolute bare minimum needed is a length of small-guage wire. I recommend 15-16 inches. You could stuff one end in SW2 on the game I/O socket then wrap the other end around pin 24 of the keyboard encoder connection and get a probably-not-too-reliable-connection. But at least there's no soldering.
There are actually various connection points and ways to do this, but I've chosen to follow the method that requires only two solder points, a mini test clip, and a 16-pin IC socket in addition to the single wire.
Let's take a look at what we need:
As you can see, these components come from RadioShack, which BTW may be going out of business in your area so stop by and get some 20%-50% discounts like I did last week!
The 16-pin DIP socket is optional if you don't mind interfering with the Game I/O port. That is, you can't easily use game paddles unless you make the piggy-back DIP socket as we're about to do (or use another connection point, in which case you're on your own).
The advantage of going this route is that it makes the shift-key mod easy to remove.
Starting with the 16-pin DIP socket and Game I/O port
Now that you have your materials, begin by consulting your Apple II reference manual to familiarize yourself with the Game I/O socket. Here, take a look at mine:
It's important to note that the diagram printed in the manual is upside-down compared to how most people look at their Apple II board, which is from the keyboard side. So pin 4 is going to be on the right side, that is, the side away from the power supply.
Take a look:
Take a look at your keyboard encoder
The other end of the wire needs to connect to pin 24 of the keyboard encoder connection. That's the pin one off from the right side, as indicated by the arrow in this photo:
Do a dry-run test if you want
If you'd like, you can do a dry-run before you solder any connections. I did this. Just stick one end of the wire directly in pin 4 of the Game I/O socket, then wrap the other end on pin 24. I typed PR#3 to get 80-columns on the display. Press Control-A to release caps-lock. Type some letters and you should get lowercase. Now hold shift and type some letter and you should see uppercase. Good!
Now turn off the Apple and make the solder connections.
Soldering
As mentioned earlier, there are only 2 solder points: one is inside the end of the mini test clip (you can take off the round end-cap). Be sure to thread the wire through the hole in the cap.
Then the second connection is to pin 4 on your 16-pin DIP socket. Make this connection as close to the plastic base as you can, otherwise the socket won't sit quite flat on the Game I/O socket. Don't labor over it, but do keep that in mind.
Here's what mine looked like:
Install your new creation
Once the solder is cooled, you can install your new single-wire shift key mod like the following photos show:
In this photo, I show the mini test clip sticking straight out, but with a bit of fiddling you can get it to go to the side to reduce the risk of it being ripped out.
And here is an overall picture of the whole thing installed in my Apple II Plus (click to see the larger image):
Test again to make sure it's still working, and now you've earned your Apple II Merit Badge for making the single-wire shift key mod!