Usually the connectors will be marked as in the picture, indicating their usage.
If your connectors do not have a label printed on them you can figure out the important ones. You will have a pair of connectors each for the power switch, the reset switch, the power LED and the hard drive LED.
The two pairs of wires used for the switches are the important ones. They can be identified with a circuit tester or multimeter (Check for resistance/Ohms). When they are pressed, the meter should indicate a connection across the two wires. In the case of the power switch if it's a really old case it will toggle on and off, so watch for the continuity to change when you press it. Otherwise the reset and power switches will only register a connection when pressed, and revert to an open circuit when released. Use your multimeter to identify which pair reacts to which swtich, and label them with some masking tape and a sharpie (or equivalent way).
As long as you identify these two and connect them correctly you'll be okay. The LEDs are not essential to booting your system and you can figure them out later. LEDs have to be connected the correct way around (usually the white wire is negative), while the switches don't matter which way they are connected as long as it's to the correct two pins. You can connect the LEDs and see which ones light up on your panel to determine which is connected where. If your power-on LED lights when there's hard drive activity, then you know that the connector plugged into the pins for HDD LED is the wires for the power LED, and so forth.
Hope this helps.
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