The I-Bus signal is part of the radio plug. It is on pin 9 of the round pin radio plug and pin 7 of the flat pin radio plug. The wire should be white with a gray tracer stripe and yellow bands around it.

Here is another test... does your radio work? If you can turn the radio on an off from the screen and change stations and volume from the steering wheel controls, then you have I-Bus in the new cable. If the radio is non-responsive, then start investigating the I-Bus wire.

Out of curiousity, where did you get the retrofit cable, and how much was it? That looks like a fantastic solution for folks doing a retrofit without having to convert a full cable.

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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