I pushed a golf wiffle(?) ball into the plug to keep a tight fit.

On my 08, parts had to supply a plastic module carrier that
is mounted behind the right rear panel to hold the lighting module.
It's not part of the kit.

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Current - 2010 X5 35d
Retired - 2008 X5 3.0
Retired - 2007 X5 3.0
Retired - 2006 325 3.0