How to Test Connector of 2015 BMW X5 to Install a Brake Controller

Question:

I have a 2015 X5/F15 with BMW OEM hitch electric controller. It has a male 4-pin brake controller connector see the attached image. I know later year models of previous generation X5/E70 use the exact same hitch electric controller with same brake controller connector. But, I have hard time to find the brake controller wiring harness with the matching female 4-pin connector. Can you help to find either the wiring harness about 20-feet to run from back to the front or the female 4-pin connector so I can make the harness with 12-and 14-gauge wires? My local BMW dealer cant help. Thank you.

asked by: Dan

Expert Reply:

We don't have a brake controller harness available that is confirmed to fit your 2015 BMW X5, but there might be a way to use the harness you have found to install a brake controller if indeed it is for brake controller installation.

What you would want to do is first verify that the harness is for a brake controller. You can do this by using a circuit tester like part # PTW2993 to test the different circuits of the connector. If one of the circuits sees 12 volts of power all the time it could be used for the power supply (black wire of the part # 90195) for the brake controller, if one of the circuits sees 12 volts when the brakes are applied and none when released that could be your stoplight switch which would get run to the red wire of the brake controller.

Now that leaves two circuit that you still would need to identify. One of them would be the brake output that would take the power from the controller and take it back to the vehicle's 7-way (blue wire from the controller) and the other would be the ground (white wire from controller).

To determine which is the ground you will want to connect the black wire of the brake controller to the power wire you discovered earlier and then try connecting the white wire of the controller to both of the remaining circuit, which ever one causes the brake controller to power up is the ground and the other remaining circuit would be the brake output circuit.

expert reply by: Jameson C