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I am very new to electrical engineering and this is my first project on it, so any help would be really great:)

I am currently trying to power an instrument, which consists of:

1) Two LEDs

2) Two Peltier elements on each side

3) Two fans to remove the heat from the Peltier elements

Here is how it currently works and how I want it to work.

How it works:

enter image description here

  • Power supply for Peltier element, fan and LED is connected with +ive and -ive wires (red and black); the remote on/off for LED lamp is connected via one +ive wire (green). So for each group (a group of 1 fan, 1 Peltier and 1 LED) there are red, black and green (2 +ive, 1 -ive) wires.
  • When supplied to external power supply (24VDC) on the red & black wires, the Peltiers and the fans turn on immediately. If the green(+ive) wire is connected to the same power supply on the positive side, the LED lights turn on.

How I want it to work:

enter image description here

  • I want to connect the remote on/off (green wires) to a different power supply, but I want to keep the red & black wires connected onto the same power supply as before (because I want to be able to turn on/off the LEDs, while Peltiers and fans would work all the time.
  • The new power supply or remote on/off provides 23.11VDC. I connect it with BNC connector and on the other end I connect it to remote on/off connector only with the +ive wire (which also might be the reason for a problem?).

What is not working:

  • When I connect the green +ive wires to a different power supply, the LEDs do not turn on.

I assume that the problem is that the green +ive wires are not anymore connected to the same ground, after I change power supply for remote on/off connector. I haven't made the instrument myself and I cannot disassemble it, so I don't know how the fans, Peltiers and LEDs are wired there together inside.

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Most likely, the Peltier units and the LEDs both share the same negative wires. In which case, you'd need to connect the negative wires to both of the power supplies.

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