The OE harness comes with the 7 pin to 4 pin adapter.

I got the last one BavAuto had in stock around 6 yrs ago, was told they were not carrying the item any longer. Had to call and speak with them to get it, item was not listed on the website.

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'03 X5 4.4 Sport, last of the M62s (8-03 build date)
I believe in deadication to craftmanship in a world of mediocrity!