I purchased the 66 21 0 303 083 ADDITIONAL KIT FOR CAMERA last year from my local BMW dealer. At that time it included the necessary wire harness, and I would be very surprised if it doesn't today.
I'm very happy w/ the quality of the OEM camera. Mine is a model or two old now (purchased in 2005), so perhaps they had better quality ones back then?
The video switchbox included in the OEM kit has 2 video inputs that I've verified. Likely it has 4 total. The input for the rear camera has 2 triggers, one for when you select Reverse, the other can be actuated at any time and automatically turns off after 30 seconds.

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2010 X5 3.5d: SOLD, but miss the torque...
2004 X5 4.4i: SOLD, but served us well

When you do the install take a lot of pictures and post a write-up please.

Mgruber,
You wanna come over and help with the install? I will try and take as many pictures and explain as simply as possible. I still need to figure out where I will install the camera on my car. None of the instructions that I have found so far really details this.

Ripp,
Thanks for confirming the info. Based on your feedback and hopefully the feedback from the parts guy tomorrow, I am going to purchase this module. It costs about $265+shipping which is much cheaper than some of the after market kits that I looked at! I am going to order from this place first and then give feedback on them. I found the link to this vendor on the Bimmerboards. The price on the ULF for my car is unreal at just under $400+shipping. I may have all my toys by spring!!

Thanks for your help folks!

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Abster641

My recommendation:

Do not fit direct in the bumper.
Fit it above the number plate, in the region of the number plate lights.
That's where the OEM camera is designed to go. It actually comes with a plate and switch that replaces the boot switch on the E39 and E46.

Reason for not using bumper: for a reverse camera to properly work, you need to see the bumper of the car when reversing to give you a distance reference on the screen.

I fitted one to a friends bumper, worked perfectly BUT it is very hard to judge distance from the screen, when you cannot see anything of your own car on the picture.

abster641 I'd love to come by to help out but I'm not local to you! Any advice I can provide though let me know!

abster641, after looking more closely at the kit contents I do NOT recommend the 66 21 0 303 083 ADDITIONAL KIT FOR CAMERA. It does NOT include the reversing camera relay and it's wire harness. As you plan to use an aftermarket camera... I would get the more expensive 66-21-0-397-639 REAR-VIEW CAMERA & SWITCHBOX.
This kit includes almost all the parts from the 0-303-083 and you do get the relay and its harness... which is needed to run up into the tailgate and down to your liscense plate area.
I'm assuming you are mounting the aftermarket camera in some custom location? It would difficult to use an aftermarket camera with the "plate and switch that replaces the boot switch on the E39 and E46" which KiwiJochen mentions below. You do NOT get this plate w/ the 0 397 639 kit.

For a good example using the 0-397-639 kit check out this write-up from www.e38.org: http://www.bimmerboard.com/forums/posts/516841

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2010 X5 3.5d: SOLD, but miss the torque...
2004 X5 4.4i: SOLD, but served us well

Thanks Ripp. Great information. The other kit is only $20 more. I will place an order for it and the parts recommended. I have a Bumble bee camera and I wonder how I attach it without too many holes. The camera I loved was this one for the mini . Do you know the part number for the plate and switch for the boot switch?

Kiwi,
Thanks for the info!

Mgruber,
Thanks for the offer to help even if you are remote:-) I can definitely use the guidance!
Thanks!

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Abster641

That one for the Mini is exactly the same kit as for the BMW - well, the camera, mounting plate and switch is the same.
Maybe the wiring loom is a different length...

Kiwi,
Would you happen to know the part number? I went to real OEM and the only thing I see the Trunk lid switch but it does not have the camera as part of it.
Here is the bumble bee camera that I plan to use.

Ripp,
Just got off the phone with the BMW dude and he says 639 is for the X3 only. 083 is no longer available in the US either. Any reason the X3 module should not work in the X5? Will the wiring harness be a problem? Because this is an electrical component once I buy it I own it so I want to make sure I am getting the right item!

Thanks!

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Abster641