Been a little while but look at #12 in the parts illustration. The cable/wire that connect the "Audio Unit" to the antenna. You will see there is an end the unplugs from the antenna itself. There are adapters that this will plug into that have will have a different end on the the other side .
Like some featured on here.
https://www.amazon.com/antenna-adapt...enna%20adapter
I am not sure what adapter you will need, but you will need one that the end of #12 goes into and has whatever end you need for your particular antenna.
If in doubt, you could try this.
https://www.amazon.com/SCOSCHE-UAA1-...ntenna+adapter
I don't know what adapter it was I used because I just happened to have one, but I think the one I had was to adapt a Kenwood to a Ford E250.
I actually don't remember if I am still using it or not. I have an aftermarket antenna now and the head unit is aftermarket.