Chosen Solution
Have a Crucial SSD that was previously in my early 2010 MBP with no issues. I upgraded to a Late 2011. When installed in the HDD port it’s not detected at all. When in a housing connected by USB it’s not detected during the boot sequence. If I boot from another HDD and plug in the SSD using USB it’s detected and readable (but not bootable according to disk utility.
You’ve hit the classic case of a broken-down HD SATA cable! You’ll need to replace it following this guide: MacBook Pro 13" Unibody Late 2011 Hard Drive Cable Replacement and this part: MacBook Pro 13" Unibody (Mid 2012) Hard Drive Cable This is the better version of the part. I would also place some electricians tape on the upper case where the cable crosses as a common issue is the abrasion against the case wears the cable over time. Do be careful at the bends over stressing them can break the foil traces inside (which is what likely happened here) As far as why the external case failed I suspect its an older SATA II (3.0 Gb/s) case. The drive your working with is a SATA III (6.0 Gb/s) which I do believe is a fixed speed drive. Give this unit a try: Startech 2.5" SATA to USB adapter
