If you get a 24 volt relay and a 12 volt power supply. You can used the 12 volt power supply to run the leds, place the relays NC and COM terminals in line on the positive wire. Then connect the relay coil terminals on to the power supply at 3J-7 pins 1 and 3. You can make a Y connector so that both sets of wires can connect to the power supply with out any modifying.
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