O.K., I figured out the wiring and control for the seat heaters(2004 Volvo S40 seats).
This is likely relevant for a lot of swaps where the new seats have heaters that are CanBus/PCI controlled. If your new seats have a 10K thermistor for monitoring temp, then this is your solution for making the seat heaters work in your YJ. I found this circuit on-line for a thermostat control, it is perfect for this application.... Craig's Thermostat Circuits
Total cost for parts was around 30 bucks for both seats combined. I was able to build the thermostat circuit on a perf board and adapt it to the original seat CanBus controller which was essentially used as an interface.
The heater elements (One on the lower seat and one on the back rest) were wired in parallel, which makes them the same as having the seat heat set to high. I was able to set the temp to 105 deg. F and control within two degrees of this setpoint. Here are some pics, each application will be different depending upon the OEM, but this will give you an idea.