If I remember right, I have mine connected to the driver side reverse light wire so it only activates when reversing (called the trigger wire I think). There should be another wire for power, then the RCA to the camera. Up front, you should have an RCA to connect to the unit, then another wire to connect to one that should say "Reverse" on it. I would rig up the connections and test before soldering, etc.
As to the mic, I think there is a setting to "activate" it. It may have been already set from the factory for me, but not on yours. I'll take a look to see if it exists or not.
This is a HUGE help!!! If you can indeed check on the mic setting...it would be greatly appreciated!!