I see a lot of questions in different areas concerning why they don't have the 12 volt power in the 7-way plug on their new truck.
I had the same problem last week with a brand new 2108 with the towing package. Turns out Ford doesn't use that pin for power anymore, it is used for their smart trailer connection. See the Ford Rep response below.
The only way I've found to correct this is to run a new line from the battery and install your own plug on the bumper and a new pigtail on your trailer to match. I actually had to run 2 so I had one to charge my breakaway battery and one to turn on lights inside my cargo trailer.
The easiest way to do this is to buy a light bar switch kit, it already has the inline fuse and relay in it. Connect to your battery, make a connection from the relay to the daytime running lights for the battery to charge and the other relay connect to your running lights so that if you forget to turn the light in the trailer off it won't run down your battery. I used a trolling motor plug at the bumper with a 4 wire connection to connect to the pigtail on the trailer. Snipped the wire going to the truck from the original trailer wire and connect wires to the breakaway battery and the other set of wires to the light inside the trailer.
a little bit of work but since they took the 12volt power from the truck connection this was the only way I could find to make it all work.
As Ford advances in technology, our vehicle systems are often upgraded and ever changing. The 7 way connector is now activated by a module which is designed to operate in the presence of a trailer with electronic braking capability. The module scans the connection to ensure all requirements for trailer towing have been met. Unfortunately, the downside to this upgrade is that the 7 way connector no longer offers a power port to any additional accessories.

The system is operating per its original design intent.

Ford Motor Company ®
Tara Dew | Customer Service Manager | FCSD

Current truck:
2018 F150 Lariat, PowerStroke Diesel.

 

How many amps does the auxillary 12V pin support? Does it cut off when they truck goes into battery saving mode? Might be an easy way to charge the batteries.

Update: I presume Ford has the center pin wired for reverse lights since they state that 12V is no longer provided for accessories.

Your comments raise another question: My 2015 appears to have the smart trailer tow connector. It informed me of a light out on my small trailer (four-way plug), and a turn signal out on my small enclosed 97 pin). I pulled our troop trailer last weekend and got the trailer disconnected / trailer connected circle jerk due to an intermittent electric brake connection on the trailer. When I physically disconnect ANY trailer I get the trailer disconnected warning.

Great feature, no one that has pulled the troop trailer the past who knows how many years (2006 Haulmark) had any idea there were issues. Crappy feature, you can't disable the chime mid-drive.

My issue: after washing the truck with the troop trailer hooked up, I got a warning message that the trailer battery couldn't be charged. Odd message since the battery is dead, but that trailer has issues thanks to tap connectors, and you monitor for overcurrent rather than undercurrent with 12v batteries.The message popped constantly until I dried out the connector, definitely sounds like monitoring for a short. Oddly, even after physically disconnecting the trailer and setting to inactive in the dash, the message persisted until the aforementioned drying.

So, if Ford no longer provides 12V to charge trailer batteries in the smart connectors, and my 2015 has a smart connector, how is it I'm getting a message that the truck has stopped charging the trailer battery? Seems they left monitoring of the 12v line for a short in place. An oversight? I did not get any trailer disconnected/ re-connected messages during while the other message persisted. Seems the 12v line is monitored for short at all times.

Also, I haven't yet checked that trailer's wiring layout, but we do have power to the interior lights.

Thoughts?

Seems Ford is pushing for off-grid capabilities for all RV's...

 

The aux line is only active when the truck detects a trailer via the trailer brake circuit. This is for all 2015 and later model years. This means people who use to use the aux line for other things like charging the battery on a trailer with surge brakes or running the interior lights in a utility trailer can no longer do this. The wire is also of a small gauge (18 or 16) so it cannot be used to charge a battery on a travel trailer or run the 12V heater on a 3-way fridge. Its only purpose is to run low voltage items like the fridge control board and maintain the trailer battery. For both of these cases the only solution is to add your own aux line from the truck battery. I did this for our old TT that had a 3-way fridge. I think Ford decided to get too smart with their Smart Trailer stuff when they didn't need to. It might make a great gee whiz item for marketing but is totally useless for the intend audience of people who use their trucks to tow.

 

An older trailer might not have the inside lights set up the way the newer ones do. The reason the newer enclosed trailers have interior lights that shut off with the truck is so you don't run down your battery if you forget that its on when you leave the truck.
The signal coming through the 12v pin is useless for anything on your trailer. It's a neat Ford feature but its a pain to a trailer owner. Ever since the trailer manufacturers got together and standardized wiring, life got easier as a trailer owner. I can remember every time we bought a new trailer or a new truck (they didn't use to come with any kind of trailer plug at all) we had to make sure to connect up all the plugs common to each other and borrowing someone elses trailer quite often meant you didn't have any working lights because they didn't wire theirs the same as you did yours.
For the people who just go down and rent a trailer at Home Depot for the weekend or day, the Ford set up is great and pretty much dummy proof.

 

The 12v charge wire has been switched since somewhere around 2000, so they really didn't fix anything. Once again the engineers outsmarted themselves.

 

I just posted about this on the other forum the other day!

The other problem is that Ford does NOT install the Fuse and Relay for the 12V powered pin from the factory. It is supposed to be installed at the dealer and is in a little plastic baggy in the glove box. I only found this out the other day.

Mine was not installed at the dealer and would not be suprised if this happened to most others as well. I didnt know this and had been towing my travel trailer around with no power going to it. My truck is a 2014 with the Max Tow package.

Here is the baggy:



Here is the locations in the owners manual:



Power Distribution Block without Fuse+Relay






Power Distribution Box with Fuse+Relay in place.

 

2014 and earlier has the dedicated charge wire. 2015 and up doesn't, which is utterly stupid .

 

I concur! But overall I do love my truck...

 

While this is true for the older models, it is not true for the current models. OP has a 2018, he has nothing to install.

 

Thanks for the clarification. Seems like Ford is getting a little nanny-state on us making a decision on when we do and don't need 12v on a trailer? A big screw you to all that have converted enclosed single axles to mini travel trailers.

I illuminate the running lights every time I pull a trailer because people = dumb. One can trigger a relay with that to charge batteries through a re-wired reverse pin, but I want to add LED's on my small trailers for backing into campsites at night. I can upgrade the running lights connection for higher current, but would that trigger an error that will annoy the **** out of me?

At that point I'd just chuck all that noise and add a 9-pin socket next to the 7-pin. Parallel wire the running, left, right, ground and reverse. Use the remaining pins for charging, accessories, flood lamps, trailer jack. Whatever one's heart desires.

Be sure to mark it: 'Not wired for use in towing semi trailers'.