One wire is 12V in and the other wire is your signal out. Your signal out is simply a lower voltage then 12V due to the resistors. The buttons simply work by changing the voltage to the headunit. E.g. Headunit recieves 3V and it raises the volume. at 4.5V it lowers the volume. I do NOT recall the actual voltages applied so do not take those two given as gospel. I'm probably WAY off base with that one.