Lost FM signal

I had to replace the antenna on my 88 Silverado and since there's only AM reception, no FM. You can't see the back of the module where the antenna plugs in so I was only able to go by feel. Is it possible there's an AM only port?

need to give a bit more information here.
did you get FM reception before changing the antenna? Possible that the radio is bad?

AM/FM both worked but FM was developing intermittent signal loss. While trying to diagnose, I pulled the antenna lead from the module in the lower dash. The lead was covered with a milkish-looking corrosion and the smaller projection was nearly rotted away. I picked up a generic replacement antenna. I get a strong AM signal but not even static in FM.

I would take the radio out and clean the hole for the antenna real good and see if that helps any