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  • Question regarding connections to a simple switch

    Hey All,
    Not too much of an electronics guy, so sorry for the n00b question.

    I have a simple rocker switch that has 3 connections on it labeled: 'power', 'load', 'ground' (that is all the info that came with it). I want to use this switch to turn on/off a second OBD-II port that I've installed in the car. I use this 2nd port 24/7 (stashed behind the glove box) and have a VAG cable hooked up to it so I can do data logging of the car whenever I please. As it turns out, I can't use the OEM OBD-II connector, if this VAG cable is powered up though (which is problematic when going for emissions, getting the car tuned by someone else, etc).

    So, my thought is to introduce this switch into the wiring between the OEM and the 2nd OBD-II port. This port has just 3 wires running to it: +12v, signal, and ground (and works 100% correctly when nothing is plugged into the primary port).

    Here's my question: what do I hook up where? My best guess:
    1. 'Power' = I cut the +12v wire I have running from the primary OBD-II port over to the 2nd port in half. The half that is coming from the primary port (i.e. the power source) is what I connect up to this 'Power' connector on the switch.
    2. 'Load' = the other half of the line from #1 above, i.e. the half of the +12v line that connects to the secondary port.
    3. 'Ground' = this is what I'm really not sure of. Do I need to connect this ground? There is a ground wire already running to the 2nd OBD-II port. Do I cut this and attach both ends to the 'ground' connection? Do I ground it somewhere else?

      TIA,
      Per

      BTW - it's a generic radio shack 12v rocker switch.

  • #2
    A switch usually has 2 connections, so I'm assuming this switch lights up. If that is the case, then the power is probably for the light, the other 2 connections are the switched leads. You can check this by getting a Multimeter and check the resistance between connections. Most likely you will just see it between the switched leads only when the switch is on.

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    • #3
      it does have a light.

      so how would i wire it up exactly if your assumptions are right? (will verify tonight via multimeter).

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      • #4
        Switches

        All you could ever want to know:

        http://www.bcae1.com/switches.htm

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        • #5
          thanks. In other words, my hunch was right.

          and i should ground the switch to something.

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          • #6
            ^ Only if you care to have switch lit while in th "ON" position (given wiring is correct)
            "In the beginners mind there are many possibilities, but in the experts mind there are few."- Shunryu Suzuki
            "Do it right or don't do it at all"

            PROGRESS:
            [-------90%-] (New Car=New Build)

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            • #7
              Originally posted by Biznatch View Post
              I'm assuming this switch lights up. If that is the case, then the power is probably for the light, the other 2 connections are the switched leads.
              in a lighted (3-lead) SPST switch;
              - the "POWER" lead is common to both the switch and the light. it provides the power input to the switch and the power source for the light.
              - the "LOAD" lead is the switched output. (it is internally connected to the light).
              - the "GROUND" lead is the ground connection for the light. (it is internally connected to the light). the switch doesn't effect this lead because it is always connected.

              NOTE: if the lighted switch uses a regular light bulb (no polarity), the "POWER" and "GROUND" leads can be reversed (to switch the circuit's ground wire instead of the power wire). if the lighted switch uses an LED, then it can only be wired as it's labelled (unless you leave the light's "GROUND" lead unconnected, in which case it wouldn't matter how you hook the other two leads up).

              F150 Truckputer [1.0] (coming soon!)
              Fusion Carputer [2.0]
              Fusion Carputer [1.0]

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              • #8
                Thanks all. Got it figured out and setup. Wiring is as per my hunch and the diagram from http://www.bcae1.com/switches.htm .

                Thanks again!
                Per

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