2015 Sierra Mic not working. Rearview mirror removed.

[bahschmidt]

I’ve looked everywhere on the internet and can’t find what I’m looking for. I’ve seen threads on this topic on here and tried all the solutions. I’ve Disconnected the battery/let it sit/discharged caps. Got a brand New mic. Dropped headliner to check wires weren’t pinched. Changed the fuse. The only thing different about my situation from others is that the rearview mirror was removed. Someone else removed it and I don’t know where it is. It’s a work truck so you can’t see out the back. But I know there’s onstar in the mirror and I’m wondering if it’s possible that the mic doesn’t work with the mirror disconnected. Any help is much appreciated or any other possible fixes that I haven’t tried. Thanks