When I picked up the trailer, my tech Kevin pointed out that my truck should have come with a Relay for the trailer that he couldn't find. The relay allows my truck to charge the trailers batteries while it is hitched and we are driving. Without it the only time the trailer will charge is when we are attached to a outlet at a campground. The batteries will power all the important systems of the trailer including the breaks (very important if the trailer comes unhitched unexpected), the lights, the water pump, the heat, the fridge and the TV or other "regular" appliances pluged into one of the several inverter outlets.
Anyway my relay was missing, since we were just waiting around I gave my dealer a call and got the run-around about the missing part. I swear 3 of the 4 people I talked to had no idea what it even was. After I got home from that trip I made a big stink via email to my sales guy and he supposedly ordered me a relay. I think it did come in but I have never gone down to get it because the dealer that sold me the truck is over 50 miles away and I found a solution right in my owners manual. It is a tiny part they should have just sent it to me.
As it turns out there are a number of these 12 Volt relays in the fuse box, one of which only operates the rear defroster so I cannibalized that one and placed it in the slot for the trailer charger! There isn't much chance I will need both to charge the trailer and defrost my rear window at the same time.