There is a connector back there, on the right hand side, behind this little vent looking panel close to the door jamb. There is a factory brake light harness available that plugs right in. If using an aftermarket system, you will need to splice into that harness, but at least you won't be needing to splice the actual tail light wires. I went with an aftermarket system, because I wanted the circuits to be isolated (self-powered). There is also a 12V lead available in that harness which makes wiring in an isolated converter easy.