In the past, I've owned a 1985 Lincoln Town Car and a 1994 Mercury Sable. Both of those cars have some of the wiring in place for options. Both had non-electric passenger seats. The TC had non-electric outside mirrors. I added those options, plus power lumbar for the Sable. It was all plug-n-play. I added AutoLamp in the Sable, as well, but I think I had to do a little wiring work myself.
I also recently added the Homelink (garage-door-opener) to my wife's 2006 SRX (it's part of the driver's side sun visor). The wiring was there for that, as well.
Unfortunately, a lot of the newer cars require that, in addition to the wiring, that the BCM also be programmed to the options on the car. I've never run into this myself, but in my DTS, I haven't added any features either. I already have the power tilt/telescopic steering wheel and it is programmed into the memory settings for the driver's seat/radio/mirrors/HVAC/etc. I don't know how well adding the option would work without programming the car's computer to recognize it. The power folding feature of the mirrors are not part of the memory programming (although the mirror adjustment settings are). That might work, if you are able to either plug into the wiring (if it already exists) or if you can successfully wire up for the folding mirrors.
I have no idea whether the wiring already exists for some of the options in the DTS or if the wiring loom is specific to how that particular car was ordered.
Hope this helps...
