I've pulled a rear seat recline setup complete, but left the wiring harness in situ as it was too involved to remove it from the parts truck. You have located the rear D-pillar blue plugs for the recline switches on your truck? If so, I'd imagine the maroon colored C-pillar plugs should also be present. Most likely tucked under the aluminum channeling that is underneath the plastic trim panels under the rear windows. That's where the main harness for that area runs.

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2005 X5 4.4i Build 04/05 Maintenance/Build Log
Nav, Pano, Sport (Purchased 06/14 w/ 109,000 miles) (Sold 8/15 w/121,000 miles)

2006 X5 4.8is Build 11/05 Maintenance/Build Log
Nav, DSP, Pano, Running Boards, OEM Tow Hitch, Cold Weather Pckg (Purchased 08/15 w/ 90,500 miles)

2010 X5 35d Build 02/10
Nav, HiFi, 6 DVD, Sports Pckg, Cold Weather Pckg, HUD, CAS, Running Boards, Leather Dash, PDC, Pano (Purchased 03/17 w/ 136,120 miles)