I had the dealership do mine and I have been mad at them ever since...
The OEM ones - if you do the upgrade will need the fusebox upgrade too - they did not always install the relays OR the header plugs into the sockets they go to on that fuseblock. If you have them great - the unit might recognize them without having to have a dealer or use a Forscan tool used to forcibly toggle the logic bits to ON to enable the Mirror or Seat heaters.
IN mine, I only had the heated seats done as an aftermarket (learned lesson in that) they bypassed and ran into the harness wiring to the seats - from the main relay. In doing so, affects the electrical in some quirky ways and since it bypasses the BCM - there is no monitoring of the seats - nor are they logical OFF state when you turn off the ignition - in some heated seat kits - the heat element if it's switched on by the physical toggle switch, remember it REMAINS on. Only saving grace was when they put it's sense power wire on the climate control relay so at least when you ran vent (no fan just O) the seats elements were off.
But if it is a physical toggle switch - not a momentary push button on push off type, you will have to find a good method to have their elements stay off once they are no longer needed. Because of the above wiring condition - the operator has the final say -- so even in the summertime if you're not careful and watch where you place things on the seat or dash by the aftermarket switches, they can get turned on. For if they get bumped on - anytime you run the Climate control - the AC or Heat - the seats are on until they are turned off by the key - in the next startup and run the seats will remain switched on even if no one is in the seat - it can get very warm ... this can make for an interesting afternoon when you or your passenger can get nearly burned by the heaters being on while in a hot car - there is no foolproof way to turn off a toggle except by ignition key or physically locating the switch and turning it off and or yanking out the wire to the switch to kill the chances of it ever coming back on when you don't want it to.
Ford set up their heated seats in a specific way to prevent inadvertently leaving the heater element on - so even when the engine is shut off - the element logics get reset back to off. So you will have to toggle it back on again, but at least you're assured it is on when you want it to be on and if you forget to turn it off - it's done for you already before you start up for your next trip.
The console Push Button and it's Tell Tale lamps and all that jazz needs the Harness pigtail to it - that number I don't know offhand. And the Relay sockets in the Passenger compartment Fuse Block are not "wired" in on mine because the car was not listed with it. Means you may have to find the jumper pigtail harness that comes from the Body Control Module that feeds into the Fuseblock and it's heavy duty current draw connector plug sockets. And requires the Forscan tool or the Dealer to enable the function thru the Body Control Module - the aftermarket the Dealer I went thru installed using the Climate main Relay as the heavy power source for the heater elements and wired the a separate switch hooked to the ignition so the electrical went dead when you shut off the car - but remained enabled all the time and worked when any setting of the climate control engages the climate relay.
The only reason why I know so much about this was due to the severe heating temperatures the seats can generate when in the summer hot sun and the AC blowing cool air and your wife can't figure out why the seats are getting so hot - she accidentally set the switch on in her seat when she got in.
Yeah, I got screwed - hope many of you out here don't go down the rabbit hole I did in believing the dealer could be trusted - they DON'T stand by their work - one shot deal and no it's not honored by FORD - if it's not on the VIN - it's not on the car...
