I needed a foot switch for my DSLR camera so that I could take hands-free pictures. On a long-shot, I went down to the local Radioshack to see if they had one. As expected, they didn't have any camera foot switches, but I did luck out that they had all the parts necessary to build my own. Here is how to throw together a 5-minute camera foot switch with easily obtainable parts from Radioshack.
Step 1: Go get stuff
You will need:
(x1) 3/32" Mono Plug (part # 274-0289)
(x1) Sustain Foot Pedal (part # 42-4053)
(x1) 20' Stereo 1/4" female to 1/8" male Cable (part # 42-2561)
Step 2: Cut the cable
Cut the cable in two such that you are left with a few feet worth of cable still attached to the 1/4" female jack.
Step 3: Prepare for soldering
Peel back the vinyl rubber jacket from the cable to expose the two audio cables and the ground sheath.
Separate the two wire from the ground sheath.
Cut away the black wire entirely and strip the jacket off the end of the red wire to prepare it for soldering.
Step 4: Solder
Open the 3/32" plug by twisting it apart.
Slide the plug cover onto the cable before you solder.
Solder the red wire to the middle metal lug and then solder the ground sheathing to the large outer metal tab.
I put a drop of hot glue in-between these two terminals to make sure that they can't accidentally cross later.
Step 5: Plug it in
Plug the foot switch into the 1/4" female socket. You can now plug the 3/32" male plug into your camera.