As far as I know, Cummins puts the block heater in all of them, but some configurations of the Dodge do not have the cord installed.
I got a cord at a local Cummins Dealer way cheaper than getting one from a Dodge dealership, but it turned out that my truck already had the cord on it, ...I just didn't look hard enough for it I guess! =O)
Here's a video of where you should find it if your truck came with the cord.