When I've converted ATX PSU's in the past (hard wired jobbys) I've stuck a 10 ohm, 5-10W resistors (those heatsinked ones with screw down tabs) on the 5V rail, and screwed it inside the case.



Also hard wire the green wire to the GND (black)


If you want a quick way to test, just stick an old HDD on one of the plugs.