How to enable the 12V output in a storageworks HS0550 psu?
It should be "relatively easy" to find the 12v source.  Since it is capable of supplying 42A, it will have wide lands going to the output socket(s).  Typically, this voltage comes out a voltage regulator (which looks like a transistor), which typically is mounted on a heat sink.  If the current is distributed, it might be the case that you have 6 regulators, each providing 7A. If it is only one, then it would be even easier to find, it is the one with the largest heat sink!
If there is no over voltage, over current protection, you might need a load resistor to be able to "see" the voltage (try a 12 ohm 25W).
Once you locate the regulator you should find one lead at 0v, one at > 12v and one at &lt;= 12v.  This last one is your 12v output source.