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Thread: How do I wire a momentary switch correctly?

  1. #11
    Newbie
    Join Date
    May 2013
    Posts
    5
    Great find, thank you ibf. Sorry guys have been traveling and had to sideline this project for a little while.
    So I've finally got it wired up and appears to be working as intended. I wired it according to ibf's diagram and appears to be correct.
    I can confirm that the +/- input for the switch illumination does in fact work in either polarity. Whether that might prove to be a problem for me or not, I don't know.
    So I have 1 additional question.

    I intend to use this switch as a momentary normally closed switch, however ideally I would like the illumination to always be on. In my testing I have found that when wired normally open the switch is illuminated until the button is pressed, at which point it illumination turns off, and vice versa when wired normally closed, the switch only illuminates when pressed. Is there any way to wire it to change this behavior, or is it just a fundamental thing with this kind of switch? I don't care whether the button de-illuminates when pressed or not, I just want it to operate as normally closed but always be illuminated. Any ideas?

    Thanks all for your help.

  2. #12
    Raw Wave
    Join Date
    Nov 2009
    Posts
    2,118
    Just power the indicator from whatever source you want ie, +12V. IGN, ACC, tail lights etc.

  3. #13
    Newbie
    Join Date
    May 2013
    Posts
    5
    Quote Originally Posted by OldSpark View Post
    Just power the indicator from whatever source you want ie, +12V. IGN, ACC, tail lights etc.
    I did. If I only hook up the +/- terminals for the indicator it illuminates, but if I then connect a power source to the Normally Closed configuration, the indicator turns off until the button is pressed. As I mentioned, the opposite happens if I wire it as Normally Open. Strange, no? Forgive, as you might see, I'm a bit of a newbie. Thanks for the ongoing help.

  4. #14
    Raw Wave
    Join Date
    Nov 2009
    Posts
    2,118
    No newbie excuses here - that is strange! IMO and from what I have seen, that + & - is for the indicator and it SHOULD be independent of the switch contacts. A multimeter (resistance range) should be able to confirm that.
    If it is NOT independent, then yet again I will blast manufacturers and sellers for not making that clear, or not supplying an electrical switching/circuit diagram.

    The only other thing I can think of is if sharing the same power source and the switch "absorbs" all the voltage - eg, because of a shared resistance from the supply.
    [ EG - my recent example - testing a 3rd brake light LED bar. 10 strings of 4 red LEDs each with its own dropping resistor. I shorted ONE LED to see the effect on brightness on its other 3 LEDs. They brightened as expected, but all other strings extinguished which was NOT expected. That could mean the wire resistance to the bar is too high (which I doubt), or an effect of the single common series diode to ground - presumably for reverse polarity protection. Though I have 2 GND wires to the bar - one to its GND thru the diode, and one that bypasses the diode - I have yet to repeat the test with the diode bypassed. ]

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