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I have a scenario where when one switched electrical path for example a tail light (LED #2) on a motorcycle is switched off, I want LED #1 to go on. When power is switched on to LED #2, then ground for LED #1 should be disconnected to shut the LED #1 off. So basically when the positive line for LED #2 becomes charged (turned on) I want to disconnect the ground or positive connection for LED #1 so it shuts off.

What would I put where the "?" mark is, a relay?

Thank you everyone for the help! Based on your feedback I think this diagram would work. LED #1 only turns on if LED #2 is off, correct? enter image description here

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    \$\begingroup\$ There's a schematic button on the editor toolbar with real electrical symbols on it including switches, relays, LEDs, batteries and earth/ground. It's very easy to use. Welcome to EE.SE. \$\endgroup\$
    – Transistor
    May 16, 2018 at 14:36
  • \$\begingroup\$ Thanks, thats good to know :). As you can tell my schematic drawing is at an elementary level at best. \$\endgroup\$
    – NYTom
    May 16, 2018 at 14:38
  • \$\begingroup\$ Your drawing is sufficient. No need to complicate things. \$\endgroup\$
    – Passerby
    May 16, 2018 at 14:54
  • \$\begingroup\$ As to if that's correct, yes. That's exactly how it should be wired. If you use bare leds and no a led+resistor or led+current limit circuit module, then you need that as well. \$\endgroup\$
    – Passerby
    May 16, 2018 at 15:05
  • \$\begingroup\$ Great thanks Passerby, yes I have resistors for the LEDs \$\endgroup\$
    – NYTom
    May 16, 2018 at 15:14

3 Answers 3

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A regular spst relay would do what you want. It would have to be a normally closed type. A spdt or dpdt relay would work as well, ignoring the extra connectors.

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  • \$\begingroup\$ I am struggling to understand how a SPST switch would work in this application. could you please explain? \$\endgroup\$
    – R.Joshi
    May 17, 2018 at 12:41
  • \$\begingroup\$ @rjoshi it wouldn't. A spst normally closed relay would. A relay and a switch arnt the same thing. \$\endgroup\$
    – Passerby
    May 17, 2018 at 15:38
  • \$\begingroup\$ I see. So one LED would be on the activating coil and the other on the "output" the relay? \$\endgroup\$
    – R.Joshi
    May 18, 2018 at 8:17
  • \$\begingroup\$ Yes. Exactly like OP shows in his second picture. Just ignore the N.O. contact on a SPDT relay. \$\endgroup\$
    – Passerby
    May 18, 2018 at 15:47
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Single-Pole-Double-Throw (SPDT) Switch, of the On-On Variant. You can also get On-Off-On which keep both LEDs off in the middle position.

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ While this is completely valid, it depends on if OP can modify or replace the switch. A motorcycle turn signal switch isn't easily replaced with a different mechanism type. \$\endgroup\$
    – Passerby
    May 16, 2018 at 15:04
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This can be achieved with a basic SPDT (Single Pole Double Throw) switch or relay.

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