Location of antenna coupling in 99 Sonoma

Does anybody know where the antenna coupling is in a 99 Sonoma? I want to install a fm direct adapter for my XM plug and play. I found a connection
about 4 inches from the antenna, but it is too small to accomodate the adapter. In my Venture there was a larger coupling under the glove box. I took the bottom of the Sonoma dash apart. I could follow the antenna from the radio to about the passenger airbag and then lost it. I followed it from the antenna through the firewall and up to the mount that attaches the dash to the frame and then lost it again. Without doing any more fruitless exploratory surgery on my truck, possibly damaging something, is there anybody that can direct me to where that larger coupling is?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.