This is my first project that I am attempting. I chose to try and make an auxiliary cable for my car to plug into my phone I bought some 18 g speaker wire and two 1/8th plugs. I soldered them up making sure I matched up the ends and after I tested it all I have is one side of the audio. Has anyone ever tried this? And where did I go wrong. Do the wires need to be swapped or did I buy the wrong wires or plugs? Help please