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I am pretty sure that this should be simple but the answer is eluding me.

Basically I would like a simple 12V DC circuit that lights one LED (red) when a power switch to a pump is off and would light a second LED (green) when the switch is on.

This seems trivial except that I cannot have the wrong LED illuminated in the wrong condition.

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    \$\begingroup\$ You don't mention what you actually need help with. Do you need help designing the whole thing? Ensuring it is 100% reliable? What is your current experience level? Have you ever built anything similar? \$\endgroup\$
    – David
    Aug 21, 2014 at 15:43

2 Answers 2

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This is easy to do if you have dual-pole (SPDT or DPDT) switch. If you do not, a simple relay with normally-closed contact will do the job.

pic

Edit: updated picture

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  • \$\begingroup\$ An SPDT switch would be simpler - connect the supply to the switch common terminal, red LED to one side, and load and green LED to the other. \$\endgroup\$ Aug 21, 2014 at 16:00
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  • RED = Pump switch on
  • GREEN = Pump connected and off
  • BOTH OFF = Pump disconnected

schematic

simulate this circuit – Schematic created using CircuitLab

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