Looking to wire an LED light indicator for my garage door. I'm in no way a lighting/electrical expert and I could use help. I do repair copiers for a living. Home auto mechanic rebuild motors etc. I have replace the entire house with new receptacles. I am a tech and work on electrical things here and there.

Here is what I need help on. I am wiring a sensor so that when the garage door opens a Led light will come on in the house to let me know that its open.

This is what I have:

  1. Transformer/ power supply input 100-24v,output 9v-500mA
  2. 3mm Pre-wired LED Red Emitting Diode DC 9-12V 620-630nm Voltage(V) 20ma
  3. Door Contact Magnetic Reed Switch closed. Max. Current: 0.5A Max. Voltage: 100V DC Max. Power: 10W
  4. 40 feet of wire

Do I need any resistor for this? or will it work fine with out it?

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  • 2
    Can you post a circuit drawing?
    – gatorback
    Commented Jan 13, 2019 at 4:54
  • 2
    It looks like there is a resistor under the heat shrink tubing. If you wire it up directly to the transformer does it light up or blow out? (I'm thinking it'll blow out). They're cheap. Commented Jan 13, 2019 at 15:50
  • I have not receive it yet. I have the power supply so far Commented Jan 13, 2019 at 16:08
  • This is all the info on this led I have at the moment. Red Pre-wired Diffused LED: DC 9-12V 620-630nm I think the last few numbers are Dominant Wavelength Commented Jan 13, 2019 at 16:27
  • I just fount out the resister is It's 470ohm. Commented Jan 14, 2019 at 4:55

1 Answer 1


If you use a plain LED, you would need a current limiting resistor. However if you use an LED panel mount pilot light, it will be as simple as drilling a hole in a faceplate and hooking up the leads.

  • Not sure if that is a resister in there already. I'm asking supplier Commented Jan 13, 2019 at 15:48
  • 1
    I see you added a picture, that sure looks like a resistor in the shrink tubing on that pre-wired LED. Still for just a couple bucks it might be worth buying a pilot light so it's easy to mount. Commented Jan 13, 2019 at 23:38
  • No room for a pilot light. Just enough for the led. Commented Jan 14, 2019 at 5:25
  • Anyone have any Ideas on this? Commented Jan 16, 2019 at 15:46

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