Rare for the BCM to die, unless you did the crap install and taped directly into the tail lights. Factory wiring is engineered to protect the vehicle from bad trailer wiring.
There are multiple layers of fuses and even fusable links. Behind the glovebox is one batch of fuses. Another under the hood. And a few fusable links as well. Test light is your friend. Don't even read the label on the fuse. Just touch the test light to both pins on the back on the fuse. Look at the fuse, the conections go all the way through. Test the fuses while they are in place. When you find a fuse that has power on one side but no the other, that one is bad.
The fusible links do require pulling.
Still didn't find it and someone still telling you it is the computer? Find the turn relays. Take one out. Two terminals are for the contacts, one should have power and the other goes to the trailer plug. The other two are for the control coil. One of those has power, the other is grounded by the BCM. Be careful playing around in there, try jumping the wrong pins and you could fry the BCM. The signal from the BCM to the relays is different than the turn signals on the truck. Part of the same logic, but has to work with the brake lights as well. So a different circuit just sharing some of the logic.
