heated seats in 2010 ford fusion

Left front heated seat     WHITE/ blue     -     HVAC control module 26pin plug, pin 5

Right front heated seat    gray / YELLOW   -   HVAC control module 26 pin plug  pin 4

From directechs

If you connect rear defrost as well it  most likely will not light up the button but you can meter the wires at the rear windshield to confirm that it is on. 

rear defrost is WHITE/ orange  - latched, in the same plug as noted above  pin12

I connected rear defrost in an 08 escape recently and it is the same color wire, but it did not light up the button.