I added and AUX connection for my car radio by soldering straight into the audio lines between the CD player and the car radio. I connected my phone to this AUX connection and added an external mic. So the 4 poles (CTIA) connect to LEFT, RIGHT, GROUND, MIC where LEFT, RIGHT and GROUND go to the car radio (connection between the radio and the CD player) and the GROUND and MIC go to an external mic.
The problem is that my phone and the CD player share the same lines so basically the cd player "sends" its audio into my phone through the LEFT and RIGHT lines. Of course, this has no effect on sound and also, I play a silent CD, but, I am having problems with my phone (android) where it automatically turns down the volume all the way to zero. I think this is happening because of a feature that turns down the volume when high audio is detected on the lines. What I thought was maybe there is a way to prevent the cd player from "entering" my phone lines? For example a diode or so..? I know that audio is achieved from change in voltage, but there must also be current I guess..? Also, could you recommend what I can do to avoid noise from the radio? I guess that it is coming from the GROUND line, so maybe some sort of capacitor on the ground line?