new here! 2000 e46 radio swap

Hi, so I'm doing a diy project on my 2000 328. I hope this is the right forum for this. As you all know the pre 9/02 radios don't support aux input. I looked up videos and pages all showing how to swap the original head unit for one made after 9/02. I ordered a new radio and an aux cable from amazon. But the issue is the back of the new unit is configured differently from my original one. There's no port for the black cable that says MD on it to go. When I unplugged it from my original radio it stopped working. When I put in the new radio it didn't work either. All the other plugs are in. What is this cable for and how do I get the new radio to work in my car??

new here! 2000 e46 radio swap