I took out the 12 cd changer two years ago and found someone who wants to buy it. I want to make sure it works but I changed the head unit and the changer isn't working with the new one. It worked when I pulled it. Is there a way to test it without tearing my new unit out?

 

What car and is this a stock changer? Normally the stock changers only work with the stock head unit unless you have an adapter.