The reason I did this was because I also made a custom usb chaging port on the left side of my car steering wheel (which is where my phone mount is) and I did not want it to be overly long. In the end it became about 10cm long and works great.
Step 1: Things You'll Need and Time
Things you'll need:
1. USB Cable $21
2. 30W Soldering iron or better $20
3. Helping Hands (Aligator clips mounted on stand, Radio Shack $20)
5. Wire cutter/stripper $5-10
6. Shrink tubing $6
7. Fine Solder (I used 0.6mm for this project) $7
8. Electrical Tape $1
9. Lighter or heat gun. $1 - $50
10. A Pin (this is not needed for second attempt)
Step 2: Cut and Strip Wire
Strip off the exterior white sheath.
Step 3: Unweave the Outer Cable
Using the a pin, work your way from the top down, unweaving the cable. Be careful not to try and unweave more than the top braided portion as the cables will get more difficult to undo as you go.
Once unweaved completely, pull to one side and twist.
INSTEAD... DO THIS:
Pull the braided cable down away from the cut. It will loosen and become wide and expose all the cables underneath. This interweaved part is just a protective layer. After pulling it back, I used sizzors to cut it off completely.
Step 4: Unwrap 'Tinfoil' and Other Cables.
Inside there are 3 insulated cables (red, green, white) and three uninsulated cables. I assumed that the uninsulated cables could be twisted together (This assumption turned out to be correct), because if there was a concern that they couldn't touch, they'd be insulated too....
Step 5: Strip Interior Cables
Strip the three cables at 3 seperate lengths. The goal is to have connection points at different intervals along the cable so it helps with keeping the cable thin, and helps stops wires crossing.
I started with the intention of having a 2" length of cable exposed, however I found this too short to work with. I will do 3" next time. (3 inches worked great)
Strip and cut the cables with 1cm of overlap. If the green cable is short on one end, it has to be long on the other to line up properly. It is extremely important that you measure the correct lengths or your cables will not line up in length after you reattach them.
Recheck the length of each cable versus the other before making cuts so you know they all line up correctly.
Step 6: Reattach
Twist one of the stripped interior cables together, solder using the helping hands to hold the cable. (instructions on soldering on youtube). Cover the cable with the least amound of electrical tape possible.
Repeat for the other two insulated cables. Make sure the length of all cables are soldered at the same length.
Solder the three uninsulated wires together.
I cut off the nylon core. It was annoying.
I wrapped the core cables back up in the existing 'tin foil' but it ended up being too thick at this point, so used electrical tape again.
Solder the exterior interweaved cables. (This is not necessary as this has been cut off)
Step 7: Cover It All Up
I had a big problem at this point. Everything was too thick so I really had to force it into place. This may have messed up some internal connections. (ON second attempt it worked fine as everything was considerably thinner.)
Use a heat gun or a lighter to shrink the tubing into place. If you use a lighter, move it quickly all around so as not to burn the tubing.
That's all folks.
I'll update this on my next attempt if it works properly or not. (NOW UPDATED)