Thanks Russlk for the reply. However, the Autocom intercom is specifically designed to take a cell phone interface cable. Using a 3.5mm stereo plug, the tip is mic, center is speaker, and base is ground. Autocom sells an isolated cable ($50) that allows you to connect a cellphone and one other audio device (GPS) together so they both feed into the cell phone interface, specifically the speaker input. So my question is how can I build this isolated cable so the two speaker connections (cell phone and GPS) are isolated from each other, yet still drive the speaker connection going into the intercom?
Thanks,