I have a 2014 Nissan Sentra. I replaced the radio from a stock radio that was very basic (didn't even have Bluetooth) to this type of radio:
Everything is working, but I cannot make calls because there is no microphone. Because my car didn't come with a bluetooth radio stock, the map lights (that house the microphone) do not have a microphone in them. So I bought a new map light assembly that had a microphone, but I don't think it'll just be remove the old map light assembly and install the new, since I assume the wires that connect the mic to the head unit aren't there.
So, I don't know how to connect a microphone to an OEM radio.
Here's a gallery with the first picture being the back of the radio that's currently in my car, and the second picture is of the microphone attached to the map lights: https://imgur.com/a/Zc2Ds78