Hi, it's my first time to post here. I built a simple 3.5mm to 3.5mm interconnect. 
First, I disassembled two rean plugs.
Then, I cut the terminals short.
After that, I got a cable with three wires inside.
I intended the red wire for right channel, white for left channel, then the uninsulated one for ground.
I soldered the wires to the plugs.
After ensuring that the connections are in place, and there are no unwanted short circuits or grounds. I applied a quick-drying, clear-colored epoxy. The one that does not conduct electricity. The epoxy will serve as cable strain relief, and to insulate the exposed leads. One plug at a time, as the epoxy tends to flow when it has not set yet, so I have move the plug around to keep it from flowing into a bad shape. Interconnect done, angled to straight.
