Here's all of the diagrams for the rear lighting. There are references to trailer tow options on some of them. Where I would start is by observing the rear lights to see if the same bulbs light up for the brake and turn signal functions. If they do, connecting the trailer wiring is a simple affair.
If you have one bulb that is for the brake light and one taillight, and a different bulb for the turn signal and another taillight, connecting the trailer becomes much more involved. If you pick one of them to add the trailer harness to, you'll have only a brake light or only a turn signal on the trailer. If you connect both truck bulbs on one side to the trailer's harness, you'll have both truck's bulbs on one side doing both functions, as well as the front signal bulbs turning on for brake lights. To connect the trailer harness there's adapter harnesses for that which include a pair of relays for each side.
By at least the mid 2000s, the "Power Distribution Center, (PDC), or under-hood fuse box, included relays for the trailer functions. One relay turns the trailer's light on for the brake function, and a different relay turns the same circuit on for the signal function, while still keeping both circuits isolated from each other on the truck. Often there was a connector in the rear to connect the trailer harness directly with no other modifications needed. I don't know which year that became standard, but check for that before you go through a lot of work with other adapter harnesses.
Let me know if this helps or if you need help with the diagrams. I'm here every night to follow up as needed.
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Monday, May 9th, 2022 AT 7:31 PM