Automotive LED Circuit

Discussion in 'The Projects Forum' started by jewster, Dec 15, 2009.

  1. jewster

    Thread Starter New Member

    Dec 15, 2009
    17
    0
    I am attempting to install some LEDs in my vehicle. They should be tied to a 3 position switch with these goals:

    POS 1: LEDs come on with dome lights
    POS 2: LEDs off, regardless of dome lights
    POS 3: LEDs on, regardless of dome lights

    I have made the following schematic. Will this accomplish my goal? Also, my leds already have resistors.

    [​IMG]
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Good effort on the schematic.
    Unfortunately, it won't quite do what you're wanting to do.
    But first, a few more details.
    Tell us about the relay - is that already existing, like the accessory circuit relay? Or are you planning on adding it?

    Did you want the lights to always be able to turn on, even with the key out of the ignition? Or just to be able to turn on when the engine is running or the ignition switch turned to the ACCY position?

    The switch: you will need a single-pole, double-throw switch that is ON-OFF-ON (center off)
     
  3. jewster

    Thread Starter New Member

    Dec 15, 2009
    17
    0
    Thanks. My mspaint skills are great as you can see. heh.

    The entire circuit is new to the vehicle, including the relay.

    Yes, I would like to be able to turn the lights on at any time, even with the keys out of the IGN and I would like that to be position #3 on the switch. Lights off, would be position #2 and lights on only with domes would be pos #1.

    The switch in my illustration was supposed to be SPDT ON-OFF-ON. I just left the middle pins empty as that would be "OFF".

    I guess I am a little confused. Any help is appreciated.

    Thanks
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    You could do something like this:

    [​IMG]

    The "Harness" label represents the wire going to the dome light that came with the vehicle.

    You'll need to find a place that is always supplied with battery voltage when the key is removed and everything is turned off. You should always use a fuse (represented by F1) to protect your wiring. Car fires are no fun.
     
  5. jewster

    Thread Starter New Member

    Dec 15, 2009
    17
    0
    Wow I was way over complicating things. That makes a lot of sense considering the draw is so low, a relay really isn't needed. My only question then, is. Do I just leave the middle pins of the switch not connected to accomplish the "off" position? If not, how would I wire the switch?

    Thanks again.
     
  6. Paragon

    Member

    Dec 8, 2009
    45
    0
    No.. you have the connections of the switch wrong in your head, jewster.

    You want an ON-OFF-ON SPDT switch. It will have 3 contacts. The center is where the LEDs get connected. The others go like SW1 is diagramed on Wookie's schematic.

    http://en.wikipedia.org/wiki/Switch
     
  7. jewster

    Thread Starter New Member

    Dec 15, 2009
    17
    0
    eesh...okay I understand now. Although the only thing that still confuses me is that the wire I need to tap to access the dome light trigger is (-). I don't need to factor that into the schematic?
     
  8. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    In my schematics' S1, the right-hand terminal is the COM (common) terminal.

    There are two other terminals; one connects to the fused battery supply, the other connects to the dome lamp power wire.

    The COM terminal is the only terminal that can connect to either of the other two terminals.

    The terminals that are not COM cannot ever connect to each other. They are isolated from each other inside the switch.
     
  9. jewster

    Thread Starter New Member

    Dec 15, 2009
    17
    0
    And it isn't a problem that my dome light wire is (-)?
     
  10. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Ahhh.... you're going to have to explain that a bit more.

    There wouldn't just be a - wire to the dome light; there would also be a +V wire.

    Or are you trying to tell us that the ground wire is switched, and the +V wire is constant 12.7v?
     
  11. jewster

    Thread Starter New Member

    Dec 15, 2009
    17
    0
    Yes, the ground is switched for the dome light, not the power.
     
  12. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Then yes, you'd need a different circuit.

    This'll take a minute or two.
     
  13. jewster

    Thread Starter New Member

    Dec 15, 2009
    17
    0
    Heh...Sorry I wasn't clear on that before. Being new at this, you can imagine my confusion and my original schematic is a result of that. I really appreciate your help here.
     
  14. Paragon

    Member

    Dec 8, 2009
    45
    0
    Change the ground to the power, power to ground, flip the LEDs.
     
  15. jewster

    Thread Starter New Member

    Dec 15, 2009
    17
    0
    I am using pre-junctioned power and ground sources so that wont work for me.
     
  16. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    You could do that, but you'd still have to insert a diode to prevent getting a ground through the dome/courtesy light circuit in reverse if the ignition switch were off.

    Otherwise, you could do this:

    [​IMG]
     
  17. Paragon

    Member

    Dec 8, 2009
    45
    0
    This board ammazes me with the knowledge here. I'll leave it to the experts!
     
  18. jewster

    Thread Starter New Member

    Dec 15, 2009
    17
    0
    Okay, but I have no idea what the stuff in the red circle is:confused::confused::confused::

    [​IMG]
     
  19. jewster

    Thread Starter New Member

    Dec 15, 2009
    17
    0
    Okay, it is a mosfet? How do i go about wiring that up? Oh man.
     
  20. Paragon

    Member

    Dec 8, 2009
    45
    0
Loading...