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General progressive lighting failures, 1987is

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    General progressive lighting failures, 1987is

    Hello friends.

    Let me start with the description of what is going on and maybe that will be enough information to solve the issue I am encountering.

    1987 325is 180k miles

    Lost power at left rear marker light.
    Then lost power at right rear tail light.
    Then lost power at instrument cluster/climate control lighting
    Then lost power at right side running lights, but not turn signal.
    All progressive, all within a day.

    I recently took the front and back trim pieces off, that house the marker lights, in the process of a full repaint.
    I also recently installed Depo Euro smileys with the city lights spliced into the flasher circuit of both forward turn signal/running lights..

    During this dissembly, the first thing that happened was one wire separated from the plug on the left rear marker light.
    I was able to replace this with used plug off a donor car.
    While I was wiring it it I lost power to that leg entirely, but started out with a good 12v.
    I assumed it was a short in the harness somewhere as I was testing and finding no power all the way back above the left tail light, where that leg connects to the harness.

    I capped that leg off (independently) thinking I would trace it back further, later, and bridge it with the right side if need be.

    Soon after, I turned the headlights on while in a car park and I got "rear light" and "license plate" warning on the overhead display.
    I checked and found my right rear running light wasn't getting power. I can't say if the right rear brake light was working but I did notice that the right rear turn signal was working.
    I tried taking the interior tail light assembly (where it plugs in) off and reinstalling with no change.

    The next time I started the car, none of the dashboard lights (instrument cluster or climate control) were working, as well as all the marker lights on the right side.
    Both right marker lights and the front marker are not working, but the turn signal is still fine on that side.


    Tomorrow I will have to go over the Bentley wiring diagram. I was hoping that in the meantime someone may have some input on this strange degradation .

    I'm thinking maybe headlight switch failure?

    #2
    While I don't think all the lighting failures are connected, I decided to just go with the most important ones and work from there.

    So far I've found that the ground at the right rear assembly is good, as all functions (reverse, brake and turn lights) work fine. It appears I am not getting power at the terminal for the running light when it is on.
    Compared to the left assembly, I am getting no voltage at that bulb using the supplied ground as well as testing with other grounds.
    I checked G300 even though this seemed unlikely, since it is shared with so many other working elements.

    I am leaning more and more towards a malfunction of the rear lights check relay as far as the right rear running light.

    I have another (relay) of unknown condition that I am going to try just to see if it makes a difference.

    I DID check ground G104 at the front left fender. It seems fine but I am going to take it off, clean and reinstall just in case.

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      #3
      As far as the taillight/tag/instrument cluster lights, there's definitely a short in the back harness.
      I found fuse 23 blown and it instantly blew when replaced.

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        #4
        Went through all the wires and may have found a bad section in one wire, the one from the light switch at terminal 12 (58K) that is supposed to go to both rear marker lights as well as C1 (KE) on the rear lights check relay.

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