Cables can have four main pairs that are Power, Reset, Pwr Led and HDD Led, you can put the multimeter in continuity or pito scale and place the tips on the pair of Power cables and when you step on the button on the panel you should click the tester , the same with the Reset pair with the corresponding panel button, in the case of the LEDs, put the tester on a diode scale and place the tips on the Pwr Led pair, the LED should light up, if it does not reverse the red tips on black and black in red, the same with the other pair ...