SSD, Macbook Pro and the cable...
About a year ago I replaced the HD in my kids MacBook Pro with a faster SSD version AND upgrade memory... did this without a hitch and then the HD started to misbehave... worked in an external boot but not in its slot in the machine. Tried SOFTWARE solutions but it had to be the cable... so got one from I-Fixit and used the guide... all done now and the machine is back in form.
Not too bad at all... the guide needs an update as key parts are in the comments -- it's the tiny orange ribbon cable that's the key... I had to rig up a magnifying glass to be able to see the clip properly. If YOU do this repair make sure you look in the comments for key info on the IR ribbon cable connector.
Ooops, I put my advice in the previous section... it's the ribbon cable to the IR that's the toughest piece. I also put some electrical tape on the base of the machine to avoid any future chafing of the HD cable.