Did you get a nav harness that you are trying to identify? If so, we can probably help sort it out. Dmonksfield did his retrofit more than a year ago, so he might not catch this post to respond.

At a high level, you have the retrofit harness described pretty well. The only exception is that I think it has the same type of radio plugs (round pin) on both the dash area and the trunk area. That is one of the reasons that many people choose the X5 fully nav/DSP harness over the retrofit harness, because the X5 harness has the BM53/BM54 plugs in the trunk. Also, the full nav harness is considerably less expensive than the retrofit harness. Finally, I am not sure that the retrofit harness is even still available from BMW.

This is a challenging project, but fortunately there are dozens of very well documented retrofit projects here and over on the Bimmerboard navigation forum. Yes, the dealer must code it, but that is spelled out in the retrofit guide; most dealers only charge 1 hour of labor for a nav recode. Also, folks have approached dealers about this project, but many dealers will not touch a retrofit. A couple guys with no prior car audio electronics experience recently completed retrofits, so this is within the capability of most enthursiasts.

Go for it 740iL, and keep us posted. Even if you get a full nav harness and not the retrofit harness. That is perfectly OK, as that harness is what many people use. Essentially, you remove the speaker wiring from the new harness, and you only have to splice over like three wires at the DSP amp plug into the new harness. You will also have to run the reverse signal and wheel speed sensor wires into the new harness, but that is relatively easy as well.

(Edited because I mis-read the dates between some of the posts.)

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2000 E38 750iL Highline Edition, Upgraded with the lastest 2006 X5 Electronics
MKIV Navigation, 16:9 Display, Bluetooth, TV/Video with Backup Camera, Sirius, and Aux Input