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Brake Light Issue Fix

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    Brake Light Issue Fix

    Had an issue with my brakelights, and Luke gave a bunch of instructions in various posts, so I went through them, edited them into one post for clarity:

    Use CRC brand electrical contact cleaner.

    Clean all the plugs that attach all wiring. The third brake light, both taillight housings and the diode board.

    Third brake light
    Clean the bulb and the contact. Replacing it with a brass base bulb may help.

    Tail Lights
    Remove both the taillight assembly backings.

    Find the ground point, where a little wire connects all of the bulbs to ground. Take it off and clean it with CRC. Use a pencil eraser if it is really bad.

    Clean the connections to the tail light backing panel, and the bulbs/sockets. Make sure the ground wire is not corroded.

    Check relay/Diode board

    Remove the left trunk liner. In front of the antenna, find and remove the 2 screws that hold the diode board. It is a small black box, about 3" X 2" X 4" with 2 plugs. It is also called the Rear Lights Check Relay Diode board, and controls the taillights. Remove the box and clean the contacts with CRC.

    Connectors in Car

    Pull the back seat and clean the ground point on the left.

    Check to make sure every single connection is nice and tight. You can use a metal pick tool to pull the connections tighter.

    Check the brake switch, located under the dashboard, on the brake pedal assembly. If you are having a "ghost failure" issue, replace the bulbs first, then the switch...even if the bulbs are working fine.

    You forgot to mention that if all fails then just remove the damn bulb from the instrument cluster and tape the overhead check panel.


      It's pretty common for the convertibles to show a brake light bulb it out, but isn't. Usually comes down to corrosion in/ on the 3rd brake light motherboard, and/ or a faulty 3rd brake light assembly in general. Also like OP stated, the bulbs. It's common for cheaper aftermarket bulbs to throw you a warning light on the check panel even though all your brake lights are working. This still holds true even on newer modern BMW models.

      1992 M tech 2 Convertible - S50 Swap
      1992 e34 Touring- S50 Swap
      1992 325i-S50 Swap

      1995 e36 M3 Mugello Red - S50
      1991 325i Convertible Laguna Green (SOLD)
      1987 325i (SOLD);1992 M tech 2 Convertible (SOLD)
      1988 325i Convertible Alpine White (SOLD)
      Brilliantrot Convertible 80k Miles (SOLD)
      1992 325i Convertible Schwarz (SOLD)
      1992 318i Convertible Project-Finished (SOLD)


        Dont forget one of the most common issues.

        Failure of the check panel system. This system has about 20 transistors that are responsible for switching the LED indicators on and off. Over the decades, these transistors begin to get stuck, resulting in the indicators being left always on or never on.

        The same exact thing happens with the SI board inside the cluster. Ever hear of people smacking the cluster to get it to work? That smack jogs the transistors. When we refurbish those check panels, after replacing the transistors, the problems go away, only problems with false report of bulb out.
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        BMW and European Electronics Repair and Restoration
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