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How to wire 3 terminal green illuminated rocker switch?

Discussion in 'Electronic Basics' started by Kasterborus, Jan 2, 2008.

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  1. Kasterborus

    Kasterborus Guest

  2. JeffM

    JeffM Guest

    If you are going to be messing with electrical stuff,
    you need to learn how to use a(n ohm) meter.
  3. Kasterborus

    Kasterborus Guest

    OK so I measured the resistance and got 35 ohms between 2 pairs of
    terminals, but 0 across only one pair - so would these be the
    terminals to connect the 125v supply to?

    This is a (hopefully educated) guess, confirmation would make me feel

  4. JeffM

    JeffM Guest

    Confirm by throwing the switch.
  5. Kasterborus

    Kasterborus Guest

    OK final question - I have a 12v DC line that I can connect to the
    third (unused) terminal.

    However I don't quite understand what is connected on the other side
    of the lamp - the two other terminals are connected to an AC line, so
    would I be able to use the 12v DC to supply the lamp?

    I don't think it's possible, what do you think?
  6. JeffM

    JeffM Guest

    If I understand correctly, you are switching 120Vac.
    So, NO. Don't do that. There is no obvious return path.

    I don't see a practical path for the lamp existing.
    You would have to use up 90% of the line voltage elsewhere
    to get the bulb to work.
    This also ASSuMEs there isn't the added complication
    that the "lamp" is a LED with a low reverse breakdown voltage.
  7. ehsjr

    ehsjr Guest

    The picture of your switch shows it is an SPST.
    That means only 2 of the three terminals are connected to the
    switch contact inside. One of those two terminals is also
    connected to the the indicator light. The third terminal is
    connected only to the indicator light.

    With your ohmmeter, find the two terminals that measure 0 ohms
    with the rocker in one position, and open circuit in the other
    position. Those two terminals are for switching the 125 volts.
    The remaining terminal (call it terminal C) connects to the
    indicator bulb inside the switch. Terminal C measures 35 ohms
    to one of the other terminals, regardless of the rocker switch
    position. That terminal is connected to the bulb inside the switch.
    The remaining terminal will measure 35 ohms to terminal C with
    the rocker in one position, and it will measure open circuit
    with the rocker in the opposite position.

    A "schematic" of your switch looks like this:

    o o-Bulb-o

    The above "schematic" does not necessarily relate
    to the physical position of the terminals on your

  8. Rich Grise

    Rich Grise Guest

    It's clearly the one against which he measured the 39 (or whatever it was)
    ohms. That is, the lamp shares one terminal with one contact of the switch.

    It will have to be wired in a way such that the common terminal is the
    12V return, either with an isolated 12V or an isolated 115.

    Apparently, in some countries, it's still legal to ground one side of the line.

    And he should check if the lamp is an LED - 39 ohms sounds like a cold

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