Hello. Yes the wires at the trunk are a known problem for breaking so that was a great place to look. You do have a relay for this as I have found documents on the interior light relay. I believe also that the light function is controlled by the general module so this could have internally failed. One thing to try if you are electronic savvy is to apply power to the lights manually to see if they will light, and check for power to the lights at the lights themselves as you go along in your diagnosis. You can also go to the light relay and manually jump the relay to supply power and see if the lights will activate or just replace it and maybe that is the problem completely. I am listing the diagrams and locations that I found and I hope it will help you. If you need more help I will try to assist you. Thank you! And good luck, I hope it ends up being nice and straight forward.
BMW Mechanic
Level 1 BMW Master Certification, 9 Years Dealer experience, Team Leader, Shop Foreman
Hello! Thank you for letting me know. Trying to trace down strange electrical problems on 850's is always a challenge. You must be pretty knowledgeable yourself. Thank you again for your accept.
-Roger
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