I finally installed the OEM hitch this weekend that had been sitting in the garage since December. Some key additional points and one question:
1. When installing the two bumper brackets [item f, #8 in the 'D' diagram in the BMW .pdf], make sure the 'long' sides point down! otherwise, the bumper cover won't fit where it meets the tailgate! Lining up those two T55, M10x85 bolts is a pain, but you can reach the T55 heads with a 'wobbly' extension on your 3/8" socket drive, lying on your creeper and looking up at the bumper.
2. When removing the original bumper, remember to leave on the two plastic caps on either end, so you can see how to fit them on the new bumper. Counterintuitive. Their function appears to be to divert rain/spray draining down the back away from the bumper innards.
3. When reinstalling the new bumper [with the end caps and cover attached], aside from 1., you need to angle the cover in the get the caps under edges of the rear corner panels, then line up the plastic clips inside the outside corners with the slide-in clips behind each wheel well, and the top of the bumper on top of the two 'verticals' on the bumper brackets. As Ed on 'wheeler dealer' sez, it really helps to have two for this function.

If you don't miss-mount the two bumper brackets and err by taking off the two end caps, this is a 4 hour job with two guys, even with the tedious job of removing all the plastic punch-pin clips.

And my electronics question. The kit comes with an electrical module [p, trailer module AHM II, shown at 19 on diagram H, and in the Circuit Diagram as X609. It mounts under the spare over the battery. Iits installation is described at 2.4, E-H of the BMW instructions. What is its function?

Finally: While doing all this, make sure you view and copy the bluetooth code from the 'motorola' white box on the rear left side. Easier to see when you have taken everything out of the cargo area ...

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