The correct (and safe) way to install lights for a trailer is with the BMW wiring harness. It powers the lights, but it also turns off the rear PDC when a trailer is connected, avoiding the annoying beeping. I believe it activates the trailer stability control mode of the DSC as well.

Some have installed the wire-tap connectors that U-Haul uses with no reported problems. Many others have had problems as you indicate. My local U-Haul facility (where I rent trailers, but not where I bought my hitch) had a note in their system regarding the X5. They recommended the factory hitch, and would install their aftermarket hitch if asked, but would not touch the BMW electrics. I asked about that, and they said that they had had to remove them too many times, and weren't interested in attempting the electrical install any longer as it cost them too much money. I filed that away. It appears your local U-Haul hasn't learned the lesson.

Recommend you buy the BMW harness. Good luck.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue