Charging pin on my 2020 F150 7-pin plug?
 

Do I need to put in a fuse or relay in order to have charging on one of the pins on my 7-pin trailer plug? On my 2013 I think I remember it coming with a fuse or relay that I had to put in under the hood fuse box to enable this feature?

You may, but keep in mind, you have to take a hundred steps to see voltage on the trailer charge pin when you are not moving.

On my '19 I did not have to. But I do have to have the truck running, press the brake so the truck "sees" the attached trailer, then make sure I get the "double honk" when I leave the truck running and fully close the door, to measure the output voltage at the trailer battery.

I have read that there are all kinds of conditions to actually see 12V on the charging pin before.

Do you know if there are steps to meet all these conditions? I was messing around with a 12V compressor and modified one of those 7pin - 4 trailer adapters that I no longer need since my truck has both so that I could pick up power from the charge pin. However it didn't work which I was expecting because I knew I wasn't meeting all the conditions to actually power the pin.

So is there a way to power this pin for temp use even if I don't have a trailer? This isn't really a big deal but I was bored one day and was playing around with the adapter. The only real use for it would be to change the pressure on my air bags without having to deal with an onboard compressor. The vast majority of the times I would actually do this though I would have my camper right there and can plug the compressor into the solar charge port which is nothing more than a 2 pin SAE connection on the tongue of the camper going to the battery. I had long ago cut off the cig adapter on the compressor and wired it to 2 pin SAE which will plug into the 4 pin side of the 7 pin adapter that I modified or as I mentioned the solar port on the camper.

Oh and for the OP. My 2018 had the fuse. Not sure if it is normally there with certain packages and not others though. It is easy to look for it. For instance I have Max Tow so maybe it is there with that package but maybe not other trucks that have the basic towing option. Well no option I guess is what it would be. I haven't seen it called out ever as being part of a given package though.

Here's one method

Arghhh. So buy a 7pin trailer harness and just hook up a bunch of Christmas Lights to it if I want to power my 12V.

I pretty much figured it wouldn't work but when I tried it I left my fob in the truck, with the truck running and the doors shut but there was no 12V but when I modified the 7 to 4 pin plug, I opened it up and moved the contact for the ground and 12V. Then I left the others disconnected.

Like I said, I knew there was more to this but for fun I was bored and thought I would try it not expecting any success and I was not dissapointed.

I just want to be able to charge the trailer batteries while running down the road. I did not find a fuse anywhere in the truck for this so it must already be in place?

On my 2018 it is fuse 30 under the hood. It is a 25A labeled "Trailer Tow Battery Charge"

If you look in the manual they will have a chart showing where it is and if it is the same fuse number on a 2020.

The relay stopped being used in 2015. The 2020 whas the "smart" controller. It has been covered a few times but here is the concept:

The "smart" trailer connector on the 2015 and up doesn't energize the charge pin on the seven pin socket unless the trailer is connected, you have set it up in the trailer menu and you have pressed the brakes after connecting it. To the OP:
1.Try to set up the trailer in the dash trailer menu and make it the active trailer. set it to "connected".
2.Connect the trailer via the plug
3.Step on the brakes once to activate the brake lights on the trailer.

Not guaranteed to work, but your best hope using the "smart" connector.
If this doesn't work, I would change the type of brakes you have the trailer set up for, ie. "electric" vs "hydraulic over electric", "none?"
then try step 2 and 3 again that way.

I hope it works for you.

P.S. also read post #20 from this thread if the above doesn't work:

2018 need 12 V out of trailer plug..??? - Ford F150 Forum - Community of Ford Truck Fans

Towing/ Hauling/ Plowing - 2018 need 12 V out of trailer plug..??? - Hi Guys: This is my first post. I just bought a 2018 F150 Lariat loaded. I have a 12 ft X 6ft Aluminum trailer with an electric battery powered hitch. I need to get 12 volt out of the trailer plug for this to work. Any ideas...
www.f150forum.com

And if you get it working and want the trailer to actually charge......disonnect the BMS connector at the battery.