How Does Brake Controller Install on 2012 BMW X5 with 4-Way/7-Way Adapter
Updated 07/23/2025 | Published 07/18/2025
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Question:
Hi, I have s 2012 x5 with the 4 pin connector that tied into the tail lights. I also have a 7 pin adapter that plug into the 4 pin and has 3 additional wires that can be used to tie in wiring for a brake controller. I saw in another question a universal harness is recommended instead. Is this because where this would plug into the vehicle doe not exist if I do not have an OEM 7 pin connector? If not would I be able to use a universal harness and then run it directly to a P3 brake controller and then use some of those wires to tie into the 7 pin plug adapter I have. Trying to figure out the best approach. Thanks
asked by: Chris
Expert Reply:
Hey Chris, you will need to hardwire in the P3 brake controller part # 90195 since your 2012 BMW X5 does not have factory brake controller wiring but the good news is you are on the right track with your 7-way adapter that has the brake controller wiring already there.
The blue wire of the adapter needs to run up to the blue wire of the P3. 10 gauge wire like part # 10-1-1 would work great. The black wire of your controller needs to run up to the positive post of the battery and the white to the ground. For that I'd go with double bonded 10 gauge wire like part # 10-2-1 and then the red wire of the controller runs to the stoplight circuit on your brake pedal that only has voltage when the brake pedal is pressed.
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on Trailer Brake Controller
Chris
7/23/2025
Thanks for all that info, that is very helpful and tells me exactly what I needed to know to get this controller installed in my vehicle.