I replaced the incandescent lighting on my Cobra trailer over ten years ago.. LEDs have improved and prices have dropped a lot since then!

I also added a 3rd brake light LED at the top of the trailer tail fin. On the Cobra, this needs to be mounted on a wedge so the light, which typically has a narrower beam with LEDs, goes back parallel with the ground.

To get the 3rd brake light to work without more wiring going to the tow vehicle, I used a 12 volt relay as a simple logic circuit. The relay coil is powered by one brake light, while the power for the relay's normally open contact is obtained from the other brake light. When you apply the brakes, both brake lights come as does the 3rd brake light. If you turn on the turn signal, the 3rd brake light doesn't come on as the relay either doesn't have voltage to the coil or to the contacts.

But, if the brakes are applied when the turn signal is also on, then the 3rd brake light will flash with the turn signal flashing one brake light. Not a problem.

bumper