The first thing to do is to buy a cheap Ebay RS-80N3 clone. You can certainly do what I describe with a genuine Canon RS-80N3 (and in fact if you do things as I describe, you will still be able to use the RS-80N3 in the original fashion). I felt better about chopping up a cheap clone. And chop one up you must, there is no way to obtain the NC3 connector that fits into the camera all by itself.
I chopped my cable pretty much right in the middle and then went to work on the half that connects to the camera. It turns out in my cable (which is unshielded) that the white wire is ground, the yellow wire is focus, and the red wire is the shutter. (The clone I have is marked "Shoot remote switch"). I used a meter (and a needle) to figure out what was wired to what. Your cable will very likely be different. In fact, depending on where the clone builders were getting wire from when they built your clone, it could vary from week to week, so use a meter and check.
If you do a search on "Canon n3 pinout", or something similar, you will find out all you need to know about this connector This excellent article tells you all you might want to know.
What I did was to wire the ground to the shield, the shutter wire to the ring, and the focus wire to the tip of a 1/8 inch (3.5mm) stereo jack I bought at Radio Shack. I can then wire a 3.5mm stereo plug onto the other half of my chopped unit, and when I plug them together, everything will work as it did before I did my chopping. See this article.
However, I can now take one of the stereo plug cables that came with my Pocket Wizard III units, and use it to connect my pocket wizard to my camera using my modified cable. And it works perfectly!
Also, now that I have a plain old 1/8 inch stereo jack that I understand to connect to my camera, a world of options opens up (beyond just saving money on this cable). If I don't want my camera continually being kept awake, I could add a switch, but what I probably will do instead is to make a second cable to replace the cable that comes with the pocket wizard, but not connecting the tip (focus). I also can contemplate building a box that will control my camera to do time lapse photography. Also, when I finally get around to automating focus stacking for extreme macro photography, the 1/8 inch connector will be right there waiting.
Here are some other links:
Apparently the camera itself uses 3.3 volt logic. The shutter and focus lines are pulled up to 3.3 volts with something that looks like a 50K resistor. The logic threshold is 1.8 volts and you will see 68 microamps of short circuit current. People have built devices that run from the 30 microamps of current that these lines can provide from the camera (see the time lapse link above).
Adventures in Computing / tom@mmto.org