I’m installing a Renogy charge controller for my travel trailer and it requires a 12v keyed on power source to turn the unit on and start charging batteries.
What I was going to do was tap into the 7 pin trailer adaptors 12v connection on the trailer side since it’s not going to be used in this instance. And it is only turned on when the running lights are turned on by the switch on the dash.
only thing I found out is that most keyed 12v circuits in my 2019 F-150 xLT are turned on when you open the doors and stay on for 15-20 seconds after vehicle is shut off.
Is there any true on /off with key in my truck. ?

 

Not sure if there is any constant 12V out back by the trailer hitch, but there are plenty of constant 12V sources in the fuse boxes.

https://fuse-box.info/ford/ford-f-15...uses-and-relay

Best way is to use a fuse tap. The small fuses are micro2. Don't borrow power from any fuse that is for CRITICAL components that would be an issue if the fuse blows.

You should use a multi-meter to determine if a slot is constant and which leg is the line side (vs load side), as that will be where the outer leg of the fuse tap should be. In the pic at the link for the passenger compartment fuse box, the line is for both rows is the BOTTOM of each micro2 fuse (install fuse tap with wire going towards the FRONT of the truck).

In the passenger compartment fuse box, slot 31 should be constant 12V (adjustable pedals).

 

I ended up picking fuse #30 on the engine fuse box.
It’s the trailer tow battery charge and is on a 30a already.
and I can tap into it from the trailer. So saves me a wire. From what I can tell it goes directly to the 7 pin trailer connector. And it is not active untill trailer is detected by plugging in the trailer plug and selecting the trailer on the dash menu. . All I need for wiring now is a 4 gauge from the tow vehicle battery and a ground. Going to connect the tow vehicle charging system and the travel trailer charging system with Anderson plugs.

 

It must be understood that all power to these locations now come from a Module that is controlled by triggering circuits and with Timing involved. Each circuit has its own fuse.
No more direct battery through switch operation except the Parking lights, and they also come through the Module. Leave these on long enough and run the Battery down. There is no timing on this function. for (2018)
The trailer connector is totally dead until the running lights are switched on, the Brakes are actuated, or the Turn signal/4 ways are actuated.
Every time I hook up my trailer, lights are tested.
Parking on, 4 ways on to look at all the lighting for any lights out.
The Parking lights was left on 3 days by another user in my absence and resulted in Battery replacement. The Battery could not be recovered by charging or even jumping. (AGM)
.
I would suggest a separate plugin Socket be mounted under the rear. # 12 wire run to the Battery location, connected to a flying lead fuse holder to Positive Battery post.
The Ground to the chassis only, not the negative post.
This way the battery management will still be involved as with the rest of the vehicle.
Connect to your controller as needed.

 

I guess I did not mention that I changed my mind and will be mounting the charger in the travel trailer.
since my solar panels are on the trailer and get connected to the controller as well.
The IGN wire (12v) needed for the module on the charge controller that I have is to tell the unit to turn on. And start using tow vehicle power.
To be able to kill my battery on my truck with the way I want to set up the 12v wire to run through the 7 pin hitch plug. I’d have to have the trailer plugged in to tow vehicle and the running lights turned on in the truck. Would be very unlikely for me to leave my vehicle hooked up like this.

 

I had to re-configure some wiring in the trailer. The circuit from the 7 pin trailer plug on the truck was connected in the trailer directly to the battery bar that has all the 12v circuits on it , tongue jack, emergency brake, tongue light ,
I just left these connected to the battery bar and disconnected the tow vehicle circuit.
This circuit stays off untill the trailer is connected and chosen in the trailer menu , truck turned on. And brakes held for minimum 3 seconds.
then the charging circuit turns on amd I get 14.5 volts through the + at the 7 pin plug.
Will work perfect to turn on the charging unit.