If you're unsure about installing your radar harness or thought it connects to the factory mirror location, here's some clarification. According to the description where you purchased the unit HERE:
it reads the following:
"... this harness will plug into your Cadillac ATS-V or ATS right under the passenger side of the dash. Remove the panel, disconnect passenger air bag light plug, then plug this new harness in between it. Then plug right into your radar detector. All Plug and Play! Less than a 10 min install!"
If you're attempting to place this unit above your mirror, that's why the harness doesn't fit. It needs to be installed here.
Here is a video of that same kind of install on a 6th Gen Camaro. Though it is for a Camaro, it is the same exact install as the ATS-V.
Hopefully this will answer some of the common questions you might have
