Turn signal behavior when hazard light switch is on AND brake pedal is depressed?

Discussion in 'Sparky's corner' started by weinh, May 12, 2018.

  1. weinh

    weinh Well-Known Member

    My starting position: Federal law in Germany requires to have priority of the hazard lights over the brake lights.
    With my 70 GS it is vice versa - when hazard is on and I push the brake pedal the stop lights are going continuously.
    So I need to change that somehow.

    My first questions is: Is it correct, that in above described situation (hazard on + brake on) not only the stop lights on the back of the car are constantly on but also both turning lights in the front?
    At least this is the case with my car and I am wondering if my starting point is "factory correct" or if I have to deal with a somewhat altered wiring.

    I have a wiring diagramm available for my car and year but honestly I was not able to figure it out by myself.

    Thanks Carsten
  2. knucklebusted

    knucklebusted Well-Known Member

    Best I remember that is normal. It is how I used to sneak home by turning the headlights off, hitting the flashers and riding the brakes to get the front parking lights to be bright. Not sure how you fix that in the GS though. No waiver for an antique in factory condition?
  3. weinh

    weinh Well-Known Member

    Thanks. No, I fear no waiver. I already need an excemption for red turn signal lights in the back. From 1970 they have to be orange in color. But no exempt at all for that hazard/brakes priority thing.

    Okay, for the moment I assume that my car behaves as it should. Here in Europe it appears strange that you can active some bulbs on the front by pressing the brake pedal.
    If the brake would only override the hazard flashing in the back and not in the front then a solution would be quite simple, but I have to figure something else out...
  4. buick64203

    buick64203 Just plum crazy Staff Member

    Is it still a law in Germany that if you park in the street overnight, you have to keep the parking lights illuminated on the street side?
  5. Briz

    Briz Platinum Level Contributor

    Would it be possible to use a switch to interrupt the signal from the brake light switch when you want to use the hazards?
  6. pbr400

    pbr400 68GS400

    I was thinking about a solution, and if legal, Briz’s idea is genius. Put a ‘bootlegger’s toggle’ switch under the dash, such that flipping it disables the brake light switch. No signal from the switch, no interruption of flashers!

    If that won’t work, could you install a couple of supplemental LEDs on the back that only serve as flashers? Or flashers and indicators? Possibly clip them to the bumper, pass inspection, then accidentally remove them?
  7. weinh

    weinh Well-Known Member

    @Briz and pbr400
    Yep, something like that but it has to work automatically, no manual action by the driver allowed (as you could forget to switch back again and then you have no brake light when you want them).
    My idea was to use standard 5 prong relays and combine them in a way, that the brake path is interrupted when both front turn signals are active. But that would require that they are flashing in the front when brake is active, which is not the case as they are continuously on.

    Yes, if the surrounding area is dark enough that oncoming traffic might oversee your car at the curbs, it is required turn on the street side parking lamps. Nowadays you don't really need it as the street lighting is good enough but back in the days that was a good thing to have.
  8. knucklebusted

    knucklebusted Well-Known Member

    The emergency flasher circuit has a dedicated flasher module. All you'd need to do it setup a relay that is normally closed to open when current is sent to the flasher. It should be possible from under the dash without too much wiring hassle.

    Very simplified diagram of what is there now:

    What you want to do that blocks out the brakes when the emergency flashers are activated. Probably only take about an hour, 2 feet of wire and some connectors:
  9. weinh

    weinh Well-Known Member

    Greg, thanks a lot.

    I am not really into that electric wiring stuff... the terminals 86 and 87 are not connected inside the relay, are they? If not, then the flasher circuit is not closed or?
    What about the attached modified layout - just tap the flasher wire and use it as trigger for the normally closed relay.
  10. knucklebusted

    knucklebusted Well-Known Member

    87 and 87a are the output of 86 trigger. 87 is normally open and 87a is normally closed.

    When no voltage is sent to 86, 87a is closed and the brake lights will receive 12v into the switch. Pressing the brakes will result in the lights coming on.

    When voltage is sent to 86, 87a will open, the brake light switch will not have power and the brake lights will not work when triggered. In contrast, 87 now has power and will run the flashers.

    Yours will probably work but I thought mine was more complete and elegant.
  11. weinh

    weinh Well-Known Member

    Let me think it through... with that kind of stuff you can easily twist my brain...
    Is my following understanding correct: The hazard flasher module is located at the upper left corner of the fuse box and is connected to 12V battery on the in-terminal, the out-terminal goes to the hazard switch (brown color in my wiring diagram). The hazard switch on the steering column connects the single brown wire coming from the flasher module to the four wires going to the turn signal bulbs, after those the circuit is grounded. Right?
    I have some issue in converting my thinking of how the hazard circuit runs into the diagram from Greg.
  12. knucklebusted

    knucklebusted Well-Known Member

    Yes, the hazard flasher is in the fuse box, top. I haven't verified all the connections but it should be quite easy to pull the flasher and find that one of the terminals has 12v all the time and the other side should be open. If that is true, my solution will work. Something like it should be possible in any case.
  13. weinh

    weinh Well-Known Member

    Could you please review the following sketch if it resembles the idea of Greg?
    Left side is wiring untouched and right I tried to translate what Greg postet.

    If so, I still could not find how to attack terminal 86. As the hazard switch on the steering column is downsteam, I have no clue where to find a hot wire to activate the relay.


    Thanks for your patience. I just want to do it right the first time and try to avoid messing up the harness.
  14. PatricksBuick

    PatricksBuick PatrickBuick

    Interesting discussion and well-known issue (over here ;-).
    Let's see if you can find a working solution to it. Does the one above still allow the turn-light to override the brake light (normal driving conditions?)

    @weinh: I would assume other's have used a different garage with more experienced employees evaluating classic cars to pass inspection.
  15. knucklebusted

    knucklebusted Well-Known Member

    I have not actually researched it. My example was just a theory of how to use a relay to cause the brake lights to have 12V cut when the flashers were on. One would need to know where the switch and the 12V source were in line. You want to be after the switch so that the 12V only is provided on pin 86 when the flashers are running. That way you will normally have 12V on ping 87a for the brakes.
  16. weinh

    weinh Well-Known Member

    As it is quite easy to realize I tried my own proposal of post #9 - and it does NOT work.
    What basically happens is that the activated brake switch is flooding all wires after the flasher with 12V, and that creates kind of a circular reference for the relay. At least it sounds like that, the relay makes an intermittent buzzing noize as it seems to open and close in very fast order. The stop lights in the back now alternate between bright and dimmed (whereas the target was bright and off).

    Not yet there but getting closer...

  17. knucklebusted

    knucklebusted Well-Known Member

    You want the 12 trigger voltage on pin 86 to be off until the flashers are activated and on solid as long as the flashers are running. If it is triggered by the flasher output, it will be a rapid on/off cycling pin 87a and of the brakes along with the flashers.
  18. PatricksBuick

    PatricksBuick PatrickBuick

    in German, sry, but that seems or at least promisses to be the solution, including a pdf wiring diagram down below.

    Pls Report back with your experience.
  19. weinh

    weinh Well-Known Member

    So, as it looks I found a solution. I purchased one, that is. A small box with a few wires to attach to the wiring harness. Following sketch shows how and as you might see, it is quite similar to what I was thinking that would work.
    From the first try, I yet have to finally install it, it seems they use kind of an electric flip-flop or time delay element in addition to the simple relay in order to prevent that shortcut humming I was experiencing.

    My German fellows might google "trennmodul kfz frost", sets you back around 60$.

    Now wish me luck that the authorities allow me to keep the red turn signal lights in the back. An american classic car with orange turn signal lights?! Exactly...

  20. PatricksBuick

    PatricksBuick PatrickBuick

    Good luck.

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