"All 6.4 PSD come with the block heater element installed from the factory but only these states have the cord in place as well:
Engine Block Heater (Std. in AK, CO, IA, ME, MN, MT,ND, SD, WI, WY)."
"If your truck was not originally ordered and shipped to one of these states, then the block heater cord was an Option that needed to be ordered with the truck. You can purchase the block heater cord from your dealer or local Navistar dealer and install the cord yourself."
If you have it, it will be on the right side of the engine bay in front of the intercooler near the hood release.