I replaced my head unit on my '04, what year is your MO?
I used the Metra dash replacement kit with the rocker and push button switches and it works great and looks just like the original if you didn't know that the switched operated differently.
I put in a Pioneer AVIC-7100NEX with a 7" screen. It works okay, but nothing out of the ordinary. It also has NAV and comes with its own antenna. I installed the Sirius XM module and antenna. I mounted the NAV on the left forward front of the dash and the XM antenna on the right front corner. They work great through the windshield.
I used the Metra SWC module for all steering wheel control interface with the head unit. I forget the brand of Back Up Camera I purchased, but it's got IR lights for night use and it's also adjustable vertically for fine tuning. It's part of a license frame. It require a power and then the video yellow cable was run to the dash. I pulled all the interior panels to get the wire up front.
I bought the park brake cheat module that lets the video player work in motion rather than with the park brake being applied.
So with all that being said, it was not an easy job finding all the wires. I was able to download a wiring schematic from the Internet and lots of wires are the same colors with slightly different stripes. The speed sensor wire was one that I had a terrible time finding. But when all done, the directions for all the components along with the wiring schematic was enough to get me through the install.
My the way, my Bose system never sounded this GREAT with the original head unit. The Pioneer has more amps to drive the Bose amps and it was worth it. I ended up with around $1200 in parts and a garage day for the install.
Check the schematic and you should find your wire. I know that I've not been much help, but perseverance will pay off.