I replaced hard drive, but still have the spinning rainbow wheel

Well, you are facing a known issue!

The first version of the cable was only rated for SATA II (3.0 Gb/s) drives which is what Apple was installing. The very last run of drive Apple used was a SATA III (6.0 Gb/s). So we often needed to replace the cable with the newer SATA III version.

The next issue is the HD SATA cables Apple used in the MacBook 2011 & 2012 systems tended to either wear or got damaged while working on the system.

Here’s a great write up on the wear issue Your Hard Drive Cable Is A Ticking Time Bomb. I encourage you to place a strip of electricians tape on the upper case as well as replace the HD SATA cable MacBook Pro 13" Unibody (Mid 2012) Hard Drive Cable. That way the new cable will hold up better!

Now the next issue is the mounting the new cable in without damaging it. This is a fragile part, over doing the bends or bending it where it is not needed is a major issue! So between the two issues I often replace the HD Cable as part of the repair when even I put in a new drive.

So we need to get an old BIC ball point pen to take the Ink straw out so we can use it as a forming brake to form the needed bends as we don’t want the radius of the cable to exceed the straws diameter as creasing it we damage the thin foil wires in it.

Here’s the needed guide to put it in Remplaza el Cable del Disco Duro del MacBook Pro 13" Unibody Mediados 2012