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Thread: Help With Weird Brake Light Problem

  1. #1
    Join Date
    Feb 2015
    Location
    Kuna, Idaho
    Posts
    736
    My Cars
    Too Many Cars (NOT!)

    Help With Weird Brake Light Problem

    New to me, 1998 750iL. There is a warning on the dash (I think - missing pixels) about checking the brake lights. Took a video of the brake lights, since I can't be in 2 places at the same time. Interesting result. It seems the 3rd brake light works just fine, but the taillights do not.

    I always thought the 3rd brake light and taillights were in (more or less) the same harness and ran from the same point, controlled by the same brake light switch, though ending at different places. This car has 120k on it and has been very well taken care of, however that does not preclude some knucklehead doing strange things. The taillights are not oem, they have clear upper lenses. I just picked up a 1998 740iL for parts, that I could swap out the light assemblies with. I have tested the bulbs (DVOM), they are good.

    Any thoughts or suggestions would be helpful.

    Thanks
    Mike Drives:
    BMW's
    E24 - 635CSiA - (1) 1985 (US)
    E24 - 635CSi - (1) 1985 (EC)
    E31 - 850iA - (1) 1991 (Black)
    E31 - 850iA - (1) 1991 (Calypso Red)

    E32 - 740iA - (1) 1994
    E32 - 750iA - (1) 1990 (Not an "L") (EC German National)
    E32 - 735iL - (2) 1990
    E32 - 750iL - (1) 1990

    E38 - 740iLA - (2) (1) 1997 & (1) 1998
    E38 - 750iLA - (1) 1998
    E38 - 740iA - (1) 2000 "Short Sport"
    E39 - 528iA - (2) - 2000 & (1) 1997
    Also:
    2015 Ram 3500 Dually, Cumins 6.7, Std.Cab. Long box 4x4 (To haul all this junk when necessary)
    2014 Dodge Dart Rallye (Daily Driver)
    2007 Mercedes Benz CL600 (Brabus SV12S)
    Mercedes Benz SL's - (1) (2002) & (1) 1999 500 - (1) 1999 600
    1967 Buick Riviera (2)

  2. #2
    Join Date
    Aug 2015
    Location
    Stockton, Calif.
    Posts
    277
    My Cars
    1999 740Il,1999 Corvette
    I put a jack handle between the seat and brake pedal, then power the seat forward till the pedal is depressed. Then I would check fuses with a test light to verify fuses are OK. Then I would test the brake light sockets themselves to verify voltage to them.

  3. #3
    Join Date
    Oct 2005
    Location
    Silver Spring, MD
    Posts
    877
    My Cars
    Too many
    Take a close look at the bulb sockets, sometimes the contacts get burned from the heat of the bulbs. Had a similar problem with my son's 98 750. Had to replace the taillight assembly.

    Sent from my SM-T817V using Tapatalk
    00 740iS
    84 635 (euro)
    88 M6
    84 745i
    88 325iX
    92 850i (6 spd)

  4. #4
    Join Date
    Feb 2015
    Location
    Kuna, Idaho
    Posts
    736
    My Cars
    Too Many Cars (NOT!)
    Solved!

    Since I can't watch the brake lights and push the pedal, I just used my phone and shot a movie. The only brake light I had was the 3rd one. Started digging around and found both outboard bulbs burned out, however both inboard bulbs tested good. Got to digging around some more and discovered the BMW harness does not use a separate wire for each bulb (inboard/outboard). The taillight itself must have those wires soldered together. The harness in the aftermarket taillights were looking for a separate wire, so there was no connection to the BMW harness. Consequently, with both outboard bulbs fried and no connection to the inboard lights, no brake lights.

    The fix. Remove taillights and connect both inboard and outboard hot leads together via solder and heat shrink and voila! We have brake lights.

    Thank you gentlemen. You helped me think outside the box.

    Regards
    Mike Drives:
    BMW's
    E24 - 635CSiA - (1) 1985 (US)
    E24 - 635CSi - (1) 1985 (EC)
    E31 - 850iA - (1) 1991 (Black)
    E31 - 850iA - (1) 1991 (Calypso Red)

    E32 - 740iA - (1) 1994
    E32 - 750iA - (1) 1990 (Not an "L") (EC German National)
    E32 - 735iL - (2) 1990
    E32 - 750iL - (1) 1990

    E38 - 740iLA - (2) (1) 1997 & (1) 1998
    E38 - 750iLA - (1) 1998
    E38 - 740iA - (1) 2000 "Short Sport"
    E39 - 528iA - (2) - 2000 & (1) 1997
    Also:
    2015 Ram 3500 Dually, Cumins 6.7, Std.Cab. Long box 4x4 (To haul all this junk when necessary)
    2014 Dodge Dart Rallye (Daily Driver)
    2007 Mercedes Benz CL600 (Brabus SV12S)
    Mercedes Benz SL's - (1) (2002) & (1) 1999 500 - (1) 1999 600
    1967 Buick Riviera (2)

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