So I mentioned this in another thread
http://www.trailmanorowners.com/foru...5&postcount=39 but there are enough late model F150 forum members out there that this bears repeating in a new one.
If you bought a late model F150, at least model years 2011-2014 (and maybe more) with the factory tow package, included with your vehicle was a plastic bag marked "AL3T-15A416-AA" sometimes the bag included instructions in it that said what the relay and fuse contained in the bag were for, and apparently sometimes it just contains the fuse and relay.
In either case, since you are a trailer tow-er, you would have quickly figured it out by looking in the owner's manual and installed them in your fuse/relay box. They must be in place in order for the tow vehicle to pass 12 vdc power back to your TM battery while the F150 is running. All other parts of 7-pin factory connection (lights and trailer brakes) are "hot," but you must have these extra items installed in the correct positions in order to have charging power to your trailer battery.
The dilemma, and the reason for this post, is if you don't buy your F150 brand new you may not get the bag, and the relay and fuse may never have been installed. When you first connect your TM to your "new" F150 everything seems to work properly. I only discovered the need for these parts because I was "fortunate" enough to blow the battery fuse while traveling three consecutive 10 hour days and couldn't keep the refrigerator cold.
Hope this helps someone else sometime....
Dave