If you have electric brakes, you'll need a compatible brake controller and install and wire it from front to back. In the back, you will probably find wires to hook up lights. I'm guessing you have a 2 filament combined brake/turn light bulb in both RV and trailer? If not, you'll need a converter to hook up separate brake/turn lights to 2 filament bulbs in trailer. You'll need two 7 pin sockets and an umbilical cord to connect the two.
If you have surge brakes, you won't need the controller.
Bob & Donna
'98 Gulf Stream Sun Voyager DP being pushed by a '00 Beetle TDI