I'm pretty much assuming the wiring is already in place, as I don't believe there are two harnesses. It looks like both underseat modules need replacement (in my case, ones WITH memory seats.) The button panel plugs into the back of the climate control. The car then has to be coded to see the addition of heated seats. The modules are controlled by the JBE/CAN network which, once coded, should work.
I haven't done much homework on this as other home projects have taken priority. However, soon I will pull one of my seats to look carefully what exactly is required. I'd hate to replace all four cushions just to make this work...but I don't want to do the aftermarket thing like I installed on my wife's Acura.