Is there any chance this case has a brand name and model number?
Normally, the little wires from the front of the case have labels on the at the connector end, where they connect to the motherboard. Are your connectors unlabeled? You should see something like PWR or SPKR on them.
The individual pins on the motherboard may have some sort of label that matches the wires---or you may have to refer to a diagram in your motherboard manual to see the pin assignments.
If not, you may be able to trace them to the front of the case and make an educated guess.
If not that, then you are down to trial and error.