12V to 0V when switch activated

Discussion in 'Automotive Electronics' started by hiimelvin, Oct 3, 2016.

  1. hiimelvin

    Thread Starter New Member

    Oct 3, 2016
    2
    0
    Hello all,

    I have a 1991 Nissan 240SX which I am attempting to retrofit heated mirrors onto.
    I am using an OEM switch that functions properly for everything except the heated mirrors.

    When the switch is up and the indicator light is OFF, the output wire from the switch to the mirrors gives 12V. When the switch is turned ON and the indicator light turns red, the output wire drops to 0V. I have tried multiple different switches to make sure it wasn't a problem with the switch, but the problem persists. My wiring should be correct as it is plug-and-play with one extra output wire to the mirrors. Is there any combination of relays I can use to fix this problem? Thank you all in advance!
     
  2. AlbertHall

    Well-Known Member

    Jun 4, 2014
    1,940
    383
    Just on the off chance, in which switch position do the mirrors get heated?
     
  3. hiimelvin

    Thread Starter New Member

    Oct 3, 2016
    2
    0
    The switch is depressed and clicks with the indicator light becoming illuminated to signify ON, but output goes to 0V. However the 12V that runs through the wire when the switch is not depressed feeds the mirrors and they begin to warm up. I tried to use a relay to get 12V from the cig. lighter when switch was depressed, but couldn't quite figure it out. Any other switch combination (choosing which mirror to adjust, etc.) has no impact on the heated mirror wire.
     
  4. AlbertHall

    Well-Known Member

    Jun 4, 2014
    1,940
    383
    You could connect the relay coil between the switch output and 12V from somewhere else, cig lighter would do. then the relay contact is connected between 12V and the mirrors. The cig lighter might not do for this as they only supply 10A and the mirrors may need more than this. Can you measure how much current the mirrors need?
     
  5. #12

    Expert

    Nov 30, 2010
    16,284
    6,797
    Maybe like this:
     
  6. AlbertHall

    Well-Known Member

    Jun 4, 2014
    1,940
    383
    We don't know that the switch supplies 12V in the off position. That 12V on the switch terminal would come through the mirrors if the switch simply disconnected the ground connection. So the relay coil should be connected between the switch and +12V and the NO contact connected between the wire to the mirrors and ground.

    upload_2016-10-4_9-21-27.png
     
  7. #12

    Expert

    Nov 30, 2010
    16,284
    6,797
    I did the best I could at interpreting the needs.
    Wouldn't be the first time I was wrong.:D
     
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