I will give as much information as I can, but my knowledge is limited.

There is a staircase with a 2 way switch. There are 10 LED lights throughout the stairs. They are using direct current.

The old LEDs were taken out and now I have 10 holes with 2 wires each. I GUESS one wire is positive (+) and the other is negative (-).

When I connect ALL of my new LEDs, each postivie to the positive wire in the wall and each negative to the negative wire in the wall, all of them light up extremely low.

After that, I tried to connect them one by one to see what happens.

To do so, I connected all the wires from the wall with each other (1st hole's 2 wires were connected together, 2nd hole's 2 wires were connected together, etc) and in one hole only, I connected my LED (tried the wires to see where it lit up, knowing this way, the positive and negative). The light that came out was bright and as it should be.

So next, I left everything as is, and connected one more LED to another hole. Once I did that, the light was again extremely low as it was when I connected all of them.

Any ideas of what is happening or what I am doing wrong?

The new LEDs are from an LED strip that was cut, and 2 wires were solder, one on the positive and one on the negative.

I am adding a schematic, have in mind I have nothing to do with electrical engineering. Just trying to make it easier to understand what I am talking about.


simulate this circuit – Schematic created using CircuitLab

For further details, if you need something I can check that have not said above, please ask me.

Thank you!

New (transformer/adapter) New one New LED new LED strip

Old (transformer/adapter) Old one

Old LED enter image description here

  • Are the new LEDs the same colour as the old LEDs? How old were the old LEDs?
    – BeB00
    Jun 19, 2018 at 9:04
  • They are the same colour but they told me they are "power LEDs". Is there a difference? The old ones where from +-2010
    – vskand
    Jun 19, 2018 at 9:09
  • They could have a different (higher) forward voltage, which could decrease the current going through them, depending on the driving circuitry. How is the DC generated?
    – BeB00
    Jun 19, 2018 at 9:12
  • I added a photo, hope it helps!
    – vskand
    Jun 19, 2018 at 9:28
  • 1
    The two transformers / adapters are completely different, you can't just replace one with another. The white one is a "led driver", it's a fixed current supply, which feeds fixed 350 mA, from 0 to 33 V. The black one is a normal DC power supply which feeds fixed (almost fixed) 12v, from 0 to 2.5 A. The wiring of the leds should be different for each adapter. If you're using the black one, you should use resistors.
    – mguima
    Jun 19, 2018 at 10:56

1 Answer 1


The original LEDs were driven by a constant-current source and were therefore wired in series.

Your replacement LEDs need to be driven by a constant voltage, and therefore need to be wired in parallel, which is how you bench-tested them.

You're going to have to figure out a way to repurpose the wires inside the wall in order to get the LEDs connected in parallel rather than in series. It may be necessary to pull new wires.

I found out each hole in the hole has the 2 cables the old LEDs used AND 2 more cables, that were wrapped together. So now I have 4 cables. Each pair, has a positive and a negative. Any idea what I should do?

That's actually good news. It means that you don't need to pull any new wires.

What you likely have is "zip cord" running from hole to hole, wired something like this (original setup):


You just need to reconnect the wires in the holes like this:


  • Did you figure that out from the two supplies? Is it 100% that they were wired in series and now have to be parallel? Thanks!
    – vskand
    Jun 19, 2018 at 13:35
  • Yes, and yes...
    – Dave Tweed
    Jun 19, 2018 at 14:12
  • Perfect, thanks, will see if that's possible!
    – vskand
    Jun 19, 2018 at 14:15
  • Hi again and sorry for the late reply. I need some more help. I found out each hole in the hole has the 2 cables the old LEDs used AND 2 more cables, that were wrapped together. So now I have 4 cables. Each pair, has a positive and a negative. Any idea what I should do? I cannot get them to light up!! Thanks
    – vskand
    Jun 22, 2018 at 13:31
  • See edit above. Let me know if anything isn't clear.
    – Dave Tweed
    Jun 22, 2018 at 21:07

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