Call an audio shop. I had the same problem when I did a head unit install on my friend's Grand Cherokee with an Infinity stock system. He called a shop the next day and it was a really simple fix, I know it was easy because even his ass did it lol. I think there is some kind of adapter piece for it, idk. Sorry I couldn't really help but if you call a good shop (try Audio Wizards) they will probably help you out.