I have followed the guides on the internet, in short to start the second PSU short the green wire on P1 with a black ground wire and the PSU will start.
This works, my second PSU does start. But if i attach any harddrives to it it turns itself off after 1-2 seconds. If i only connect fans or nothing it will remain running.
If it mathers the PSU is from colermaster. They're both ATX powersupplies, and i have tried to use 2 different ( But same brand/model) PSU as the second PSU.