Before I start tearing apart the rear of my console, and/or removing the rear seat to look for the harness, I have to say that my X5 didn't come optioned for rear seat heat. So, would there even be 12v power to pin 86 (of the non-existent relay) to furnish power to my rearview dash cam, without a switch to activate it?
my X5's option list

I don't know if BMW even installed the wiring harness in all X5's, or just when optioned for it? Some mfg's do, some don't, use universal harnesses.

Even if the harness is there, then I'd still have to complete the circuit where the missing rear seat heat switch isn't.


Anyway, the cigarette lighter socket extension cable will be here today, and I'll probably go that route (a quick fix), until I'm ready to do some retrofitted wiring.

Update, 2 hours later: Installed! camera comes on when I press the splitter/voltage gauge switch (as does power to my front camera (old Samsung Galaxy J327A, from 2017), the power for my 8" tablet, used as a"dashboard" for the Torque Pro app), and charging power for my main phone + two others. Only 6 inches of the cord is visible, but it sits under my travel bag (containing diagnostic tools, specialty tools, lithium-ion jump box, and EDC items) that is always in the right rear floorboard. I've never had more than one passenger in the rear seat, so it's not a big deal.

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01 BMW X5 E53,3.0i-5L40E, 7/13/01
topas-blau,Leder-grau,"resto-project car"

Here:
14 Lexus ES350,3.5L-U660E
09 HHR Panel,2.2L-4T45E
04 Chevy 2500HD,6.0L-4L80E
98 GMC Sierra 1500,5.7L-4L60E

Gone:
66 Chevelle Malibu 2dr ht.,327>441c.i.-TH350>PGlide/transbrake
08 Cobalt Coupe,2.2L-4T45E
69 & 75 C10s,350c.i.-TH350
86 S10,2.8L-700R4
73 Volvo 142,2.0L-MT4
72 & 73 VW SuperBeetles,1.6l-MT4
64 VW,1.2l-MT4
67 Dodge Monaco 500 2dr ht.,383c.i.-A727
56 Chevy 210 4dr,265c.i.-PGlide