Sure they will! Stick it to the frame behind your rear tire or somewhere.

 

LOL I hate it when that happens.

 

Just discovered this by accident yesterday as I was reaching in just to grab something. With the truck completely off, if you pull the turn signal lever, the head light come on. Not sure if they turn off by themselves. Hopefully they do.

 

That is the 'flash to pass' operation while driving.
Interesting that it switches on the lights. I'll have to give that one a try.
Do you have "auto lights" and if so, is that enabled?
I'll try it with my truck in both modes.

 

Yes my auto light is enable.
I can see this coming handy.

 

I would like an indicator for this as well but from what I have read, early 2015's had a warning come up on the IPC that said the tailgate was open or something to that affect. There was a TSB because of erroneous messages and Ford's solution was to disconnect the switch that triggered the indication, then they stopped installing the switch altogether. So from my understanding, later model 2015's and up do not have the switch installed. I have a 2015, not sure of the build date. I may open up the tailgate this spring to see if the hardware is installed, and if it is, I may try to get this working. I have a tonneau cover and the only way to tell the tailgate is down is to walk around the truck, or shift to reverse so the camera comes up. If the tailgate is down, the warning beep goes off continuously and all you see in the camera is the ground under the tailgate.

 

I think it was the early 2016’s that had the tailgate warning light.

 

The 2016 I am driving was first sold in March 2016. Unless the computer was flashed at some point disabling it, I do not have that feature on a 502a.
It would be good to know. It's not different today than it was 30 years ago, but for some reason it feels right to make sure to know the gate was down.
Have only tried to pull away once with gate down. Fortunately I was aware when backing up from the parking space and the steady tone alerted me (backup camera).

I've left the gate lowered from the garage on previous truck a few times only, in nearly 9 years. Usually it has been after loading my bicycle to go riding...forgetting to close the gate while finishing gathering gear.
Same with this truck, that one time, was completing my post ride activity and forgot to flip it up.

 

As I am led to believe the tailgate warning alarm was triggered by a ‘switch’ built into the left side tailgate latch. It was a grounding switch that triggered the alarm and put a warning flag in the instrument cluster window. I understand that it failed so often that it was discontinued. The Forscan entries are there to reactivate it, but a switch of some type is required. It can be enabled to work as a grounding circuit (the safest in my opinion) or as a hot circuit. I set mine up as a grounding circuit using a micro switch attached high on the side of the box. My setup activates if the T/G is opened about a quarter inch. I have a topper so the gate would not fall easily but it still could not be latched. I found the wire that is presently not connected under the rear of the truck, ran it to the switch and then to ground. Works like a champ! I’ll look up the older threads on this and put them in another post. It is a little work but the results for less than $5 is worth it.

 

Do a search for "Tailgate Ajar Warning" and you will find many threads on this. Add tailgate warning to 2018 lariat or something like that has many pictures. This should be a lot of help.