That is unreal if your 3500 Cummins does not have a the cold weather group. If it does not say it on the sticker than I imagine you will not have the heater element installed. The plug in for it if you have it will be near the oil filter.. I will snap a pic here in a few for you.
Edit: Okay so I had some already...hmm. Anyways here you are
This first one is near the passenger tow hook. That is where my plug is on my 2012 2500 Laramie.
This picture is showing where the plug in for the element is. As you can tell I have the cord so it's there. The big gray thing to the right is the engine oil filter.