Once you remove the light unit leaving the carrier in the vehicle (See my article.) you will find there is a built in recess to take the OEM ballast. All you need is the retaining bracket and screw for it. (Again, see article for part numbers.)

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2021 X5 xDrive40i
2015 X5 xDrive35i MSport
(Traded) 2013 X5 xDrive35i