Relay wiring notes

5V Relay module working but LED not turning on – How to wire?

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I’m trying to control a relay from Raspberry Pi that will switch an LED on/off. The relay is working (lightning up and clicking), but the LED doesn’t turn on.

Here is how I wired everything:

VCC – 5V

IN2 – GPIO pin 19



COM2 – 9V Battery Positive side

I’m aware that the way I wired NC and COM are probably wrong and I would like to know how I should wire the LED side so that it can be controlled from the relay and Raspberry Pi

Thanksledrelayshareedit  follow  close 1flag asked 45 mins agopatriciajlim11add a comment

1 Answer



  1. How to use Rpi to control a relay to switch on/off a LED?
  2. How to wire the NC and COM terminals of the relay?


Let us use the following example and look at right side, the relay switch with the COM, NO, and NC terminals:

relay and led

Notes on connecting the COM and NO terminals.

  1. COM (Common) – The COM terminal connects to the power source, eg +5V, +6V, +9V, +12V of a battery.
  2. NO – (Normally Open) – The NO terminal connects to the load, ie the LED, with a series protecting resistor, usually 4k7 to 1k2.
  3. Grd – (Ground) The ground terminal connects to the other end of the load.
  4. NC (Normally Open) – The NC terminal is not used, ie, left open or disconnected.

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