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OBD2 and Blink light

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  • OBD2 and Blink light

    Been doing a bit of research and just wanting confirmation before I carry this out.

    This is on a B2 90 with a 3b engine and Motronic ECU, I havent found my Diagnostic sockets yet and suspect I dont have any so will be tracing the cables from the ECU loom, either way if I find them or not I will be fitting a 16 pin ODB2 socket.
    I want to make a portable blink light which will be on an OBD2 plug.

    I will be connecting as per the first photo and the blink light will be connected as per the second photo, ill fit a momentary switch for the jumper.

    Question 1
    My understanding is that the 3rd connector from the right which is the blink signal is a negative? If so does that mean I can use any of the 'Manufacture Specific" pins as per photo 3 and it wont cause any issues if any other diagnostic equipment is plugged in due to being a negative?

    Question 2
    What is the reason for the resistor in the blink light diagram? I have some 5w LED 501's that I was hoping to use one for this.

    Question 3
    If the resistor is required what size do I need?

  • #2
    The MIL blink signal is a negative but not sure about putting it into an unused OBD2 pin?
    You would most likely be ok but better to avoid any issues with OBD2 equipment connected later on.
    The MIL blink signal (ECU pin 22) could be taken to a dash mounted LED so when you use your switch it’s a permanent feature in the car rather that a portable blink light.
    Then your OBD2 port will be as normal with K (ECU pin 55) and L (ECU pin 13) with a 12vdc supply.
    Resistor is just for limiting current into the LED I would just get a low current 12vdc red led that wont require resistor that you could mount on you dash in an alarm bezel or just have it dangling in the glove box.
    Would be cool to fit switch and lamp in a spare heated window or hazard switch to give you the 4sec momentary switch and a MIL lamp in a combined unit.
    Was going to do that myself but never got around to it.

    blink led.jpg led.jpg


    • #3
      OK thank you, as you say making the MIL a permanent item may actually be a better option