Take one of the ATX extension cables and carefully remove the cable ties.  Take care not to damage the insulation of the cables.

Looking from the back of the socket with the clip recess uppermost the pin numbers have been clearly marked.

Once you have removed the cable ties locate pins 14 and 15 and cut the cables, leaving the tails as long as possible attached to the socket.  We now need to locate pins 7 & 8 and cut the cables about 2.5 inch (60mm) long, again leaving the cables attached to the socket. Remove all other cables, cutting them as close as possible to the socket.  Bare the ends of the four cables by about 10mm (3/8").  For an easy way to strip cable take a look at our hints and tips page

Insulation is one of the most important aspects of this project, do not overlook any part thinking you will be safe.  Accidents do happen and if something that is capable of turning out this kind of current arcs then it could quite easily cause a fire.

It is important to seal the cut ends of the cables.  I used silicone sealant for this.  Run a bead of silicone over the end of the socket and smooth the silicone using a wet finger.  See hints and tips

Once the cable joints have been made it is important to slide the heat shrink insulation over the joint and heat it with a cigarette lighter until the insulation has shrunk tight to the cable.  Keep the lighter moving to avoid burning the insulation

We will start by connecting pins 7 and 8 of the Slave PSU socket.  Cut a length of heat shrink insulation, slide it over one of the cables and push it down as far as possible.  Do not skimp on the insulation, cut it about a 1.5  inch (40mm) long.  To see the correct method of jointing cables see hints and tips

Once you have soldered the joint pull the heat shrink insulation over the joint and warm it with a cigarette lighter. 

Left: is a photo of the slave PSU socket  the joint made and insulated.

We will now connect the two PSU sockets together.  Take the second ATX extension and cut the cables from pins 14 and 15, approximately half way, then bare the ends of the cables.  Slide a length of heat shrink insulation over the socket end of the wire.  Flick the ends of the wires to open up the individual strands and mate all three cables from pins 14 ensuring that the socket from the slave PSU  is at the same end as the plug from the master PSU.  Twist the strands together and solder the joint ensuring you do not blob the solder on (otherwise the insulation will not feed over the joint).  Pull the insulation over the joint and heat it.  Repeat this step for pins 15, don't forget to slide a length of insulation onto your cable first.

Once you have completed this fasten a cable tie round the cables, just below the joint at the plug end, and pull it tight.  Bend the socket for the slave PSU back up so that both sockets are next to each other and fasten a cable tie close to both ends