I have a very interesting situation - here a couple months ago I would consistently get a defective lamp warning whenever I would place auto shifter in reverse - all bulbs and fuse checked good but no reverse lights coming on - then about a month ago the wind blew the red cover lens off the right rear brake light a210 820 46 64 off - I had an extra so I replaced it and even though the reverse lights are not in that part of the body but rather in the trunk lid - replacing that break light assembly temporarily fixed the defective lamp warning - now it is coming back on but again only when 98 E300TD is put in reverse. I don't think it was coincidental - how can the rear stop tail light have anything to do with the reverse lights when they are in different light assemblies - is there a wiring diagram available?

Sounds like you have a back up light issue going on.

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Jim

Probe the contacts with an oldschool testlamp on the bulb holder to see if you get it to light up with shifter in reverse.

If it doesnt light up on ground or power side check the flexible wiring harness near the hinge of the trunk lid, thats a usual point of failure.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

Don't know about the rest but on my year and model the back up light switch is combined with the Neutral Safety Switch.

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84 300D, 82 Volvo 244Gl Diesel