Is it possible my truck didn't come with one? There is a picture of a rear window on one of my control knobs and when I press the knob a light comes on I thought indicated a rear defroster, but nothing seems to happen. I looked at my paperwork and there is no specific mention of rear defrost. Is it possible I don't have it? I can't believe they would build a crew cab truck without it. Any info would be appreciated. Thanks.