Turning on a 300w computer power supply.

mneary said:

I would use a 12V automotive bulb such as SAE1156 single filament stop light on the 5V line. It won't glow real bright, and won't get unbearably hot.

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I usually connect 1 or 2 CPU fans to the supply, and that's enough to keep the ATX supply on

Short pins 13 and 14. Job done. (Yes, green to ground in other words.)

Have you tested the supply to see that it's good? It really needs testing under load - we found that even with an ATX tester, because it wasn't under full load a PSU could be reported as good, but wouldn't work when used in a system.