Where is the Logic Board Test Point?

I'm trying to get to the bottom of why, on my diagnostic LEDs, #2 lights up briefly then shuts off when I try to power on my Mac. For older models, I've read this warrants a need to replace the power supply, but sometimes it's not that cut-and-dry, and I'd rather not blow $65-80+ on barking up the wrong tree, because if it's a bad logic board, I'm saying goodbye to Macs forever.

So I'd like to test the logic board...but where? And what pins are what? I've only found test points of other models, that show 14 pins. I see a power input port from the PSU that has 12 pins, but that's it. Is that the test point? Please, someone help! Thanks in advance.