Sorry but it's a case of trial and error when they are like that. If you had a multimeter and new how to use it you could test for volts at the MOBO plug from the PSU from the back of the plug, while it switched on and connected to mobo.
PS they are all low volts in the Comp. only 240V in power supply back of the plug would read on the pins any where from +5 to +12 or -5 to -12 volts
It's a lot easier on a bench