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Thread: Help Need to Isolate Electrical Issue

  1. #1
    Join Date
    May 2013
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    South Florida
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    My Cars
    1994 BMW 525i

    Help Need to Isolate Electrical Issue

    Hello everyone, I'm having an issue that I hope could be resolved with a little additional brain storming.

    **Summary at the bottom**

    I have a 1994 525i 5 speed. I turned on the car a week ago and was presented with a tail light warning on the dash. No big deal I thought since I always carry extra bulbs with me. I then notice that both tail lights are off. I check to make sure my brake lights work and they indeed do. I then check the bulbs for both taillights and they are both looking good.

    I begin at the basics with checking the fuses and all the ones for the taillights are fine. I then get into the trunk and begin looking at the wiring for the light since sometimes I carry a lot of cargo in the trunk. Everything looks good.

    Today i realized something interesting that appears to be related. Both of the rear marker lights were also off.

    As I grab my multimeter, where should I begin to look first?

    **SUMMARY**
    94 525I 5speed
    Both taillights and rear marker lights are not functioning. (checked fuses)
    Brake lights come on, license plate, and inside trunk lights are all functioning.
    Need help from those that are more familiar with the electrical system.

    Thanks!
    [IMG][/IMG]

  2. #2
    Join Date
    Dec 2004
    Location
    CT, USA
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    4,161
    My Cars
    e28, e34, e39
    Do the front park lights work?
    I would first check for power on the grey/yellow and grey/violet wires at the light switch and then proceed from there.
    demet

  3. #3
    Join Date
    Nov 2017
    Location
    Canada
    Posts
    8
    My Cars
    1995 525i
    Currently have the same issue. Going to be looking at it tomorrow

  4. #4
    moroza's Avatar
    moroza is offline MORΩN ΛABIA BMW CCA Member
    Join Date
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  5. #5
    Join Date
    Mar 2017
    Location
    Sweden
    Posts
    19
    My Cars
    520d F11
    some trunk cables broken around hinge

  6. #6
    Join Date
    Nov 2011
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    Riverside, CA
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    My Cars
    01 M5, 93 M5, 94 525iT
    ^^^^That would be where I'd look first. The sedans have the wiring in only the driver side trunk hinge, while the tourings have wire looms in both hatch hinges.
    Tommy L.

    (
    oOO \ (IIII) (IIII) / OOo)

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  7. #7
    Join Date
    Jun 2009
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    Macon, GA
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    '94 530iT/A|'95 540iT/6
    Quote Originally Posted by moroza View Post
    You need this.
    Came here to post this. It's all in there.

  8. #8
    Join Date
    May 2013
    Location
    South Florida
    Posts
    71
    My Cars
    1994 BMW 525i
    Thanks for all the input everyone!

    It ended up being a combination of two things.

    1. There was a single wire that had snapped along the hinge of the trunk which has now been fixed.

    2. These tail lights are not OEM (Depo) and the plastic around the bulbs on both tail lights had cracked which caused the bulbs to move and prevented contact to the wires.
    (I know I can't believe both were bad!)
    [IMG][/IMG]

  9. #9
    Join Date
    Apr 2016
    Location
    Santa Clara, Ca
    Posts
    67
    My Cars
    1993 525i
    Cool thread, helped me repair my trunk lightning. Very cool person/s sharing this info. Went right to the problem and fixed it.
    Is there any particular reason bmw's designers decided to allow such a weak point? Makes me kind of concerned about the rest of the wiring. And then, any other failure points I need to be concerned about with this 93 525i that I need to know about?

  10. #10
    Join Date
    Jun 2009
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    Macon, GA
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    '94 530iT/A|'95 540iT/6
    There are 40 or so wire splices under the back seat fuse box as well as under the carpet of the rear driver's side footwell. If you have any odd electrical gremlins, check there. Moisture has been known to collect there and corrode the splices.

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