Trailer brake controller

The Sprinter is a bit more complex to add a brake controller to. As the system is multiplexed the brake signal needs to be intercepted before the control module under the drivers seat. On our 06 even though the seven pin wiring was there from the factory it did not include a brake wire. Using internet resources I was able find a wiring schematic and then tie into the circuit before the multiplex controller. Some have simply added a second brake switch on the pedal linkage and used a standalone circuit.
You really need to research this for the newer model Sprinter and be aware that most likely the trailer will not interface with the Sprinter anti-loc system.