repurpose a psu for a project

I’m in the process of converting a dead mac (logic board) into a retro gaming machine i have purchased the lcd driver and all is working well but i want to be able to use the iMac power supply i have it all connected up and have 1 12volt line that is permanent but can not figure out how to power up the psu most if not all psi’s can be jump started by shorting out pins only info i can find is to do with pc power supples 24 pin rather than this 14 pin one.

The psu i have is OT8043