I have included a picture that shows the typical location of the factory connector on Toyota vehicles that use brake controller wiring harness # 3040-P.
The factory connector should be located underneath the dash, to the left of the steering column, taped to another harness near the emergency brake pedal. However it is possible that it could also be behind the kick panel to the left of the emergency brake pedal.
I have also heard that it can be more towards the center console hidden above a large black air duct and that you will have to reach up and feel for it. If you find it here there is not a lot of space but should be enough to plug in the 3040-P harness.