Why motherboards have two pins for LEDs, led+ and led-
If the LEDs are driven using the most common method, as shown below.... you have no commons, no Vcc and no Ground.

If you have more than one LED you can not join any of those wires together either.







simulate this circuit &ndash; Schematic created using CircuitLab

Note: you could swap the LED and resistor to generate a common plus side. However it is usually better to have the resistor on the high side to prevent inadvertent shorting of the Vcc to ground, or elsewhere, in a bad or faulty cable connection. Also, if the cables are any significant length, attaching a long antenna directly to the power line adds EMI, EMC, and static discharge issues.

However, either way you would label the pins LED+ and LED- so whomever is creating the cable or attaching the LED knows which way round it goes.