Do you have the VGA-PWM adapter too? Like this one https://www.amazon.com/GELID-SOLUTIONS-PWM-Adapter-Cooler/dp/B005ZKZEQA. You need it to hook it up to the mini PWM connecotr on the GPU. Might as well just try with that first. Unless your OEM card has different connector type, in which case you're gonna have to modify the original connectors. Had to do that with a Sapphire nitro+ card, kind of a hassle but got it working fine.
Anyway it's gonna be a worthwhile upgrade when you get it working, love the universal nature of the G12+aio.