2 years ago I bought a 1m Canon OC-E3 TTL flash sync cable. I’ve used it once since then. The main problem being, having my flash at an arms length away from my camera is not much of an advantage, coupled with the fact that the cord itself is coiled you do not really get a 1m length as it will never fully stretch it out. So after a bit of reading on the web I decided to extend the length myself. Turns out it is pretty easy.
Tutorial
This tutorial will show you how to extend the length of your TTL flash cord. The cable I used is for Canon cameras and flashes, but from what I understand the procedure should translate over to Nikon, Sony, and other brands quite easily.
Materials

- Canon OC-E3 TTL Cord (cut in half)
- 10m of Cat5 cable
- Speedlite - Canon 430EXII (any Canon ETTL compatible flash will suffice)
- Scissors
- Electrical tape
Method
1: Cut your sync cord in half. It is best to cut it in the middle, as you will need to strip about 3cm of sheath off the cord, so if you make a mistake you will still have plenty of cord left. When you remove the sheath there will be a wrapping of copper strands underneath. This is to shield the wires when they transmit signal, you can cut these off as they will not be needed. There will also be a wrapping of copper strands around the red wire, this WILL be needed, so unravel them and twist them together (see below).
2: Once you have exposed the wires inside the outer sheath, strip the cladding off the individual wires and twist the ends (see below). Repeat this step for the other half of the sync cord.
You can see in the picture below I have 5 wires that have cladding and 1 wire that is bare, this is the wire that was wrapped around the red wire, treat this as the 6th wire.

3. I used 10 metres of standard Cat5e comms cable as my extension. All we need to do is make a pathway for the flash signal to travel, so we need to provide straight a link between the two cut ends of the sync cord. Cat5 is perfect for this because its consists of 8 colour marked copper wires and is used to transmit data (which is what is being sent to your flash). All of the ‘Cat’ type cables will work as long as there is at least 6 individual wires inside, the only difference between them will be the distance the signal will travel, you will only need to worry about distance issues if your are making an extension upwards of 20-30m.
Cut your cable to desired length, then strip the outer sheath off to reveal the 8 colour coded wires inside. Pick 6 of these colours (e.g. I used: blue, blue/white, orange/white, orange, green, green/white), and strip the cladding off them to reveal bare copper wire.
Do the same for the other end of the cable making sure you pick the exact same colour wires.

4. With your Cat5 cable and sync cord, get a wire from each, and twist the exposed copper strands together tightly (see Fig. A below). Repeat this for every wire. Make sure you join the EXACT combinations at each end. If the wires crossover anywhere the flash signal will not transmit correctly and your flash WILL NOT FIRE.

Fig. A in the picture below shows the ‘6th’ wire which was the one wrapped around the red wire in the sync cable. Remember to treat this as a normal wire so join this to the 6th wire in your Cat5 cable.
Fig. B shows the copper strands that were wrapped around all the wires. You can cut these off as they will not be needed.

5. Once you have joined all the copper wires together wrap electrical tape around each and every join covering all exposed wire. This is to shield the wires and prevent them from touching each other thus breaking the circuit (see Fig. A below).

6. Tightly wrap tape around all of the joins, binding them together. Make sure you overlap onto each end of the cable to ensure the join will be solid.

Once you have taped up both ends you are done! You now have a fully functioning TTL flash sync cable!

Heres a shot of the sync cord in action. Flash fired at a sync speed of 1/2500sec on manual high speed sync.
EXIF: 1/2500sec | f/6.3 | 10mm
I hope you enjoyed this tutorial, please feel free to share it around. If you have any problems just email me and I’ll do what I can to help.
-Jason