The wiring schematic is included in the installation instructions for the hitch. I have attached a copy of the one on this site; it is from 2000, but the trailer module itself didn't change (the wire colours may have). The instructions show the Euro hitch ball, so the wiring may be slightly different for that reason, but the basics should be the same.

http://www.bmwmotorsports.org/pdf/e5...iler_hitch.pdf

There is a legend right before the schematic. I see a couple of fuse holders in the schematic. One fuse would just be too easy.

Following the principle that what has been added on is the most likely thing to have failed, I would remove the fuses, then disconnect and reseat the plug in the trailer control module, and the one in the wiring to the hitch. I would also buy a test light at an autoparts store for $3.

Hope you're not reading the PDF on a cell phone.

Good luck.

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