1 
1 Installed a HDD in optical bay, but then primary SSD wouldn't work...
After trying a few configurations, I currently have my SSD, (which works fine, tested externally and internally) installed in the optical bay and a HDD in the hard drive bay. The HDD works briefly and then disconnects/ejects, I wasn't accessing when it does this.
I have read that running the OS from the optical bay isn't ideal so I want to move it to the hard drive bay, which doesn't seem to want to read it.
Does this sound like I damage the hard drive cable?
Please tell us about the drives. Have you ever replaced the HD/IR cable?
mayer さんによる
Most likely your HD drive cable is worn out as Mayer pointed out but you could also have a second issue here. I would also review the notes in OWC's product: OWC Data Doubler. It makes no difference who's device you used the issue is within the MacBook its self.
Dan さんによる
It was the hard drive cable - new one installed and it seems to be working fine.
Had some minor booting issues as both drives had a Recovery partition and it didn't like that. Deleted the partition from the secondary drive and boots as it should.
Thanks Everyone!
Paul Taylor さんによる