Each white LED runs on ~3.3vdc. Each red LED runs on ~2.2vdc

A unit setup to run on 24vdc will be running very dim at 12vdc if at all.

They are typically setup in a combination of series and parallel. You just need to find the 1/2 way point of the 24vdc setup, split it and add a second 12vdc line to that place. You will also have to add a resistor in series with the new 12vdc line.

24/ 3.3 = 7 in series white LED's.
24/ 2.2 = 10 in series red LED's.

A pic would help figure out the needed resistor too.

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