Thanks to everyone who posted info in this thread. I could have sworn my truck didn't have one. I looked all over the front of the truck, around both tow hooks, everywhere, and could not find the plug. Thanks to you guys, I went to the oil filter and saw the cord and was able to follow it up front. The plug had just fallen way down into the bumper and I had missed it before. It's been in the teens at night the last week, and although the trucks starts right up in the morning, I'm sure it will be happier plugged in.

Thanks again guys!