Good luck, LVM! The OEM hitch kit is very well-made [by Westphalia in Tennessee, it appears], and everything fits together very well, though close tolerances, and you have to fit certain things together all at the same time to install. I expect you are right about the plug-in X609 trailer module. If you have the backup warnings, you already know to be very careful when taking off the old bumper to unplug the wiring harness inside the cargo area and at its rubber grommet so as not to pull the wires out of the sensor unit(s). Note the kit comes with a warning sticker about 'no brake controller', to be added to the hitch if you don't have a controller; note also the rec'd limits on length/height of the hitch ball/shaft in the OEM instructions. I'm still leaning toward the RF version of the Tekonsha Prodigy brake controller, which requires not wiring in the vehicle, as we'll be moving the controller between my X5 and the CEO's Mercedes diesel ML .....

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2006 X5 3.0 6-spd w/Evo UUC ssk
sport/premium pkgs
born Valentine's Day, 2006.