Ehh its not working.
Positive to positive.
Negative to negative.
2 pin power wire connected from Opus to MII
I connect the ACC-ON wire to 12v positive, nothing happens. I don't see a green LED either. I can't even find it on the Opus, it's definitely not lit up though. Fuse is not blown.
Does the needle go up on the battery charger when you connect it to the battery? If it doesn't your battery might be dead - happens if they are left discharged for a while.
Do you have the ATX connector plugged in too?