Wiring a subwoofer in a 2019 truck.
 

I'm wiring an aftermarket sub woofer and have found the wiring to be unlike the videos I have found. There is no longer a WPT 1212 connector receptacle to hook up to. I've found the harness for the left rear door and the + and - speaker lines but haven't figured out which wires are the REM turn on (used to be blue) and the small ground that goes with the high level input lines I am using. Anyone know the colors for those 2 items?

Have you figured it out yet? I'm having the same issue.

You may want to go to crutchfield.com and see if you can find the info.

https://cimg2.ibsrv.net/gimg/www.f15...fbded9e04c.png
Crutchfield was no help. Here's a color code explanation supplied by dbmachine I wired it to the left rear speaker wires in the harness that runs up the rocker panel.The matching WPT 1212 plug was an unnecessary purchase. It was also unnecessary to get the Forscan unit to turn on the remote power wire (blue). I ran a blue wire of my own with a power cable up the passenger side rocker panel to avoid any interference to the sound cable. I attached the blue remote power to fuse # 23 in the panel under the passenger side kick panel. The power in this fuse stays active when the truck shuts off during the Auto Start/Stop feature and your subwoofer will stay on. The small black speaker ground, I attached to the body behind the rear seat. There is another ground attached there next to the seat upright catch.
I attached the small speaker ground to a spot behind the insulation, behind the rear seat, where another ground is placed already.

I’m about to buy a 2019 xlt and currently have a jl sub setup in my Silverado that I don’t want to part with. I also don’t want to put a new head unit in the new truck. Is it possible to adequately run an amp and sub off of the stock f-150 xlt head unit? -Mike

My subwooer was powered so I didn't need an amp. Mine's an XL with a stock head unit. I suspect you could do that but I'm not an expert. Check all the videos you can find on Youtube. They were helpful except the WPT 1212 plug they refer to no longer exists on the 2019s.

Left subwoofer plug in behind back seat panel
 

I have a 2017 F150 Xlt super crew, I found the plug behind the seat which I believe is for a factory subwoofer that my truck did not come with.

My question is, can I just tap into those wires for the sound signal to rca converter to my amp and have it work or do I need to go to my ford dealer and have them activate the subwoofer function?

Someone (you or the dealer) with Forscan needs to turn on the blue remote power wire that powers up the subwoofer independent of the actual power cable. Or run your own blue remote power wire from fuse #23 behind the kick panel on passenger side.

My amp turns on from the remote wire that comes off of my rca converter and I figured that would be enough, I do have sound but it is very minimal. I will try and connect into my fuse #23 and see how that goes.

If your amp has a remote wire, you're all set. If your truck has an auto trans with auto start/stop the subwooofer may shut off at stops.