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Thread: Gray-Backed Cluster Woes

  1. #1
    Join Date
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    11/87 735i & 735il P/C

    Gray-Backed Cluster Woes

    Hello all, big progress today!

    I finally have working fuel/temp gauges along with the obc display and mileage!!!

    When I first got the car, only the tach/speedo and various indicator lights worked. I did some research and came to the conclusion that the capacitors were the most-likely culprit. I sourced the caps and paid an electronics professional to replace them. No change!!

    At that point I gave up for a few months. Today I was feeling inspired (and sick of not having a fuel/temp gauge), so I swapped in a known-working cluster from my 1988 735il parts car.

    Still nothing but tach/speedo.

    At this point I was frustrated and feeling defeated, but I took to google and did some more research. I learned that on the gray-backed earlier clusters, the mileage and other info is stored on a chip in the brown connector that plugs into the back of the cluster. At this point with the knowledge that my problem was NOT the cluster itself like I originally assumed, I decided to swap the connector as well.

    Success!!

    Well, kind of... Everything is working (save for the OBC display needing a new bulb on the left side), but of course now the mileage shown is from the parts car... at 226,698k miles.

    Working Cluster.jpg


    Does anyone know if this brown connector thing can be repaired? Specifically the chip inside. I'd really like to have the true mileage shown (>50k).
    Last edited by CamE32; 06-19-2018 at 05:33 PM.
    1983 4-spd Mercedes 240d w/403k - Sold!

    11/87 E32 735iA w/45k - Daily Driver (finally!)

    04/88 E32 735iL - Parts Car

  2. #2
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    You need to find someone who can read out the old code plug HML 075, but this is not a standard version like the other EPROMs http://bmwe32.masscom.net/johan/299960/299960.html
    Maybe the easier solution is to install a blue or white back version and reprogram the EPROM to the original data such as VIN, miles etc.
    Might be worth to ask in the forum car audio and electronics, maybe there is someone, or the forum diagnostic software
    Shogun tricks and tips for the E32 series are HERE!

  3. #3
    Join Date
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    Thank you Shogun!

    I was hoping it was something a little simpler, like bad solder joints or weak contacts. Should I risk prying it open?
    1983 4-spd Mercedes 240d w/403k - Sold!

    11/87 E32 735iA w/45k - Daily Driver (finally!)

    04/88 E32 735iL - Parts Car

  4. #4
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    I have never opened it, you can try if you want. Maybe you find a solution. If you are lucky, maybe just a broken wire.
    I see in your pic that the warning LOW BEAM is there and the low is not that bright as the beam. That could be caused by a bad contact of the bulbs. Slightly slap the dash if the light comes back. If so, I would remove the cluster, remove all the bulbs, clean the contact surface of the bulbs + counterparts with a glass fibre electrical contact cleaning pen, and also rebend the bulb socket metal pieces and also clean their contact surfaces.
    Had the same problem on my cluster this week.
    Shogun tricks and tips for the E32 series are HERE!

  5. #5
    Join Date
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    Thank you Shogun! I think I'll buy all new bulbs soon, as the tapping method has no effect. As an aside, I got rid of the LOW BEAM warning with two 50watt 8ohm resistors. Now I'm curious if 25watt would suffice because the 50watts get insanely hot!! I'm worried they could come loose from their mounting points and start a fire with any prolonged contact with plastic.



    Do you have anyone in mind who might be willing/able to work on the old brown code plugs? I'm too afraid of permanently breaking something to open it up myself.
    1983 4-spd Mercedes 240d w/403k - Sold!

    11/87 E32 735iA w/45k - Daily Driver (finally!)

    04/88 E32 735iL - Parts Car

  6. #6
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    Maybe you ask in the software forum, if there is someone, which might be able to work on it.
    Shogun tricks and tips for the E32 series are HERE!

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