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Turn Signal and Side Marker in the one bulb?

Discussion in 'LEDs and Optoelectronics' started by CMA, May 12, 2017.

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  1. CMA


    May 12, 2017
    The problem is how to use 1 light bulb for both turn signal and side marker.

    I did research a lot of things I can search but not able to find the best solution. I would not like to use too many relay and wires because I don't want to make my car into the processor.

    Here is the original diagram... pretty old technology but still fine as new turn signal flasher... (will update in the future)


    Here is what I am trying to add SPDT relay to turn off Side Marker while duringturn signal or hazard on.

    (light blue and pink are added/modded.)

    V1 (complex and ignore any errors)


    The real problem... Only works if Side Marker enable... so how to Turn Signal during Side marker disabled haha...

    V2 (simpler and still ignore any errors... just sketch)


    It's impossible to do completely disable the Side Marker during Turn Signal enable. I decide to dim the Side Marker so Turn Signal will light more brighter..

    No I don't try or test this in the real life yet...

    It would be appreciate if you can give me some points how to do allow both SM and TS to use one bulb...

    as far as i know the solution is
    - This v2 digram
    - Dual wired bulb (probably not the best idea since both light will be same bright amber)
    - Switchback light... (still use dual wired bulb)

    Thank you

    BTW my English is not that great so please bear with me.
  2. CMA


    May 12, 2017
  3. shrtrnd


    Jan 15, 2010
    I don't know what you have, but if this is a single element bulb, why don't you wire-in a dual filament bulb and separate the incoming signals. I suppose it won't help with what you want to do (it won't dim or turn-off the side marker), but it's an idea you might think about.
  4. Bluejets


    Oct 5, 2014
    Old English cars (Wolseley, Morris) used to do this (single filament-dual purpose) with the rear tail light. Maybe find something on the web there.
  5. CMA


    May 12, 2017
    Yes as the diagram show single filament bulb. But issue for dual filament bulb is possible same indicator due to both TS and SM are amber colored light... It would be hard to recognize for other driver.

    I check Wolsely Morris a bit and it's pretty less known and I am not able to find its light diagram.


    I also check this diode but it's very unclear how it works to me because I thought the diode only allow the flow in the right direction. I don't understand how it does cancel other power.... maybe that diode is acting like capacitor? (store and release the power supply)

    And I know that diode have some flawless design especially heat waste. That's why MOSFET exists.
  6. Bluejets


    Oct 5, 2014
    Quite simply , it won't work.
    Circuit shown is a basic steering diode arrangement.
    As shown it will work with one input or the other without disrupting any other circuitry BUT when both are active the light will just follow the continuous "on" signal.

    What you will have to do is use the blinker enable line to disable the side light signal.
    Using a small relay would probably be the easiest.
    Last edited: May 13, 2017
  7. Bluejets


    Oct 5, 2014
    Had a closer look at your post but I cannot see what drives the park/turn in the original.
    Not clear exactly what you are trying to do as the original seems to cover it.

    Apart from that, the mosfet link is a good idea.
    What they are doing there is simply using a P channel which is normally turned on and running normal lights through it. When they want the turn signal to turn the single filament on and off , they simply use the turn signal to the gate of the mosfet to turn it off and hence the bulb flashes.
    As they say, P channel is normally in the on state without any gate voltage.
    Drawback is the running light has to be on.
    To get either of your left or right signals from the indicator to operate the mosfet, then use the other "steering diodes" to isolate the turn signals from eachother.
    Diagram below......may need slight mod to match your circuit as I cannot see the whole thing and as many auto wiring systems are earth return.

    Hope this helps......not tested

    Attached Files:

    • L_R.jpg
      File size:
      96.1 KB
    CMA likes this.
  8. CMA


    May 12, 2017
    My car has two bulbs for each SM and TS therefore I want to merge wires to connect to the only one bulb.

    Original SM is not included so it's part of Illustration light diagram as it will active as I switch SM on.... basically same as lighting diagram... That's why I add that diagram on my V1 and V2. (I won't use those diagram since MOSFET is much better anyway)

    According to your diagram... both L and R can't be in same wire... therefore I will 2 MOSFETs for each SM and TS.... (It will works for only one SM so need another one for other SM... hahaha.)

    AND about R1.. how much resistance is that? for D1 as normal diode? and last... no feedback or waste energy release right? I aimed for very efficient and simple diagram like your diagram!

    Appreciated for very simple diagram...

    Thank you very much for explaining.
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