OK so my 2010 Escape is in for a transmission recall, and i'm having the alarm system tweaked because its falsing all the time. I got to talk to the guy who the service manager said was the most knowledgeable guy they have when it comes to the vehicle electronics, computers and systems - what we can do and not do.
Because the vehicle is so computerized now, everything works together, and is controlled by the main processor in conjunction with the 2 sub processors - the one that runs the climate control system and the instrumentation system, connected by a low speed bus. Everything from the power windows, headlights, power locks, interval wipers, ALL the displays are all on the low speed databus.
The systems are uploaded with your purchased options that are linked to your VIN number, so if something needs to be replaced, they just enter the VIN and the exact part will be shipped.
They have experimented with adding options after at the customer's request. Like the message centre (a change in the instrument cluster to include that function, plus the buttons on the dash), like the temperature indicator on the side of the infotainment (radio) display, like adding Sync after.
Their results were poor, the problem is they dont have any control over the processor programming, they can't just go to a webpage and click "yes" to the outside temperature display. What they CAN do is find a vehicle that has your features PLUS the one you want, enter the VIN into the computer, and download from Ford the BIOS for the vehicle computer systems. They then upload that into your vehicle and VOILA. Well almost. He said what happened was the computer started kicking back some error codes. Some would put on the check engine light. Some would give error codes on the message centre display in the instrument cluster, and some would show errors in the radio display. He said the problem is the BIOS that gets uploaded, also has some other things in it for features or systems that are not listed, but are assumed on that VIN package. So the computer cant find a sensor for something, or cant find a damper motor etc etc.
So he said yes you can, but you might need to spend a lot of cash at the dealer trying to find a VIN BIOS that makes the computers do what you want to do, without any errors. You might find you will need to add the Sun sensor in the middle of the dash plus the interior temperature sensor plus the external temp sensor etc.
Lastly, he said that for the most part, the engine harnesses are the same from model to model, and the under-dash harnesses are the same. But the In-Cabin and outside harnesses are built-to-VIN for the features you have, and they started doing that "a few years ago".
With all that in mind, it might be cheaper to buy the whole dash including all the components including the computers and harnesses from a wrecker and hook everything up. Or start looking on the lot, find the one with the features you want to add plus all the features you already have, and ask them to upload that VIN bios into your vehicle after adding the required sensors, and maybe some unrequired ones.