Your engine was originally equipped with the block heater and the cold climate package. The block heater is located on the drivers side of the engine block in one of the freeze plug holes, the cord runs forward from there along the drivers side frame rail to the front of the engine compartment on the drivers side.
I am sorry, the gasoline engines are on the drivers side and the diesel engine is on the passenger side. I do not have a diagram of the cord itself. Here is a diagram of the heater location, you can follow the cord forward from there.