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How to Connect Trailer wiring for 2013 BMW X3  


Hi. My BMW has one wire driving the tail and brake bulb. The signal is a separate wire. Both bulbs are 1156 style. However, the tail/brake bulb draws 4 volts for tail, then 12 volts for brake. The 1156 bulb is a single pole/filament style. Will the flat 4 wire harness work? If not, what do you recommend? Thanks.


Helpful Expert Reply:

Your 2013 BMW X3 has a Pulse Width Modulation Stop/Tail (PWM ST) wiring systems, sometimes called Multiplex wiring. The Curt Powered Tail Light Converter with 4-Pole Flat Trailer Connector # C59236 will work with your X3, but it has to be installed a certain way for all the lights to function properly. Since you already have done some testing and identified what kind of system you have it will be easier and quicker to get installed.

You need to test and identify the color of wires for each function on your X3, stop, turn, and tail. There are 5 wires that come out of the converter box in the wiring kit, and they should be hooked up as follows :

Green wire - splices into right turn signal wire
Red wire - splices into stop/tail signal wire
Yellow wire - splices to left turn wire
White wire - connects to vehicle ground
Brown wire - Not used (or grounded with white wire)

I prefer to not use the quick splice connectors in the kit and use Deka Butt Connector # 05731-5 anytime that I have to splice any wires. It provides better protection for the wires and is more secure.

One big advantage to installing wiring in your BMW is that the battery is in the rear hatch; so routing the power wire from the converter box to the battery will be much easier than if it were under the hood.

I linked a video of the wiring install on a different year X3 but the process will be similar. I also attached a copy of the instructions showing you how to hook up the wiring for each type of system it works with.

expert reply by:
Robert C
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Will the CURT trailer module fool the CANbus system on the BMW X3 ?Thank you.

Etrailer Expert

Chris R.


The Curt harness won't affect the CAN bus system on your BMW in any way. All vehicle functions will continue like normal with the trailer wiring installed.

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