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Heated washer unit sounds like a fantastic idea.
If you ever had the standard blue stuff freeze on you, it's a pita trying to deal with that crap during a long drive.
The big connector is for your long decommissioned heated washer fluid unit. They were recalled early on and the customers given a refund. Between your cigar lighters you will have 4 or 5 buttons, one of them being for this feature. I cannot remember if someone is making them again should you wish to make it work.