I have a loudspeaker for my car and I've added an aux cord to the system so that I can play music over it. There is also a microphone attached to it and what I've done is add a 3 way switch between the two so I can either use the microphone or the aux cable. I don't really like this setup and I want to be able to use both at the same time but I'm a software engineer, not electrical, so I'm not sure if tying the voltage of the aux and microphone to the same input is safe.
Here is a diagram with what I currently have:
And I want to remove the switch:
My roommate suggested adding diode to ensure the signal only goes one way but said that would lose about .7 volts. I don't like that as the input isn't that strong already and I have to manually amplify music in audacity so that you can hear it. While I'm asking a question, does anyone know how I would go about amplifying these signals through hardware because the microphone you really have to scream into and the aux is generally pretty soft compared to the tones/sirens it can generate. Unfortunately I don't have the schematics to the circuit board which is probably needed for something like that.
Here are some pictures of the circuit board/system: Circuit http://zyphox.com/misc/pa1.jpg